docs: add code editor documentation

content/docs/code/index.mdx

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+---
+title: Code Editor
+description: Reactive code editor for Pyreon — CodeMirror 6 with signals, minimap, diff editor, tabs, lazy-loaded languages
+---
+
+# @pyreon/code
+
+Reactive code editor built on CodeMirror 6. Signal-backed state, lazy-loaded languages, custom minimap, diff editor, tabbed multi-file editing. ~250KB modular instead of Monaco's ~2.5MB.
+
+## Installation
+
+```bash
+bun add @pyreon/code
+```
+
+Peer dependencies: `@pyreon/core`, `@pyreon/reactivity`
+
+## Quick Start
+
+```tsx
+import { createEditor, CodeEditor } from '@pyreon/code'
+
+const editor = createEditor({
+  value: 'const greeting = "Hello, Pyreon!"',
+  language: 'typescript',
+  theme: 'dark',
+})
+
+<CodeEditor instance={editor} style="height: 400px" />
+```
+
+## Signal-Backed State
+
+Every piece of editor state is a reactive signal:
+
+```tsx
+// Read reactively
+editor.value()        // current content
+editor.language()     // current language
+editor.theme()        // current theme
+editor.readOnly()     // read-only state
+editor.cursor()       // { line: number, col: number }
+editor.selection()    // { from: number, to: number, text: string }
+editor.lineCount()    // number of lines
+editor.focused()      // has focus
+
+// Write — editor updates automatically
+editor.value.set('new content')
+editor.language.set('python')
+editor.theme.set('dark')
+editor.readOnly.set(true)
+```
+
+## Configuration
+
+```tsx
+const editor = createEditor({
+  value: '',                    // initial content
+  language: 'typescript',       // syntax highlighting language
+  theme: 'dark',                // 'light' | 'dark' | custom Extension
+  lineNumbers: true,            // show line numbers
+  readOnly: false,              // read-only mode
+  foldGutter: true,             // code folding
+  bracketMatching: true,        // bracket matching + auto-close
+  autocomplete: true,           // code completion
+  search: true,                 // find & replace (Cmd+F)
+  tabSize: 2,                   // tab width
+  lineWrapping: false,          // wrap long lines
+  highlightIndentGuides: true,  // indent guide lines
+  placeholder: 'Type here...',  // placeholder when empty
+  minimap: true,                // code overview sidebar
+  vim: false,                   // vim keybinding mode
+  emacs: false,                 // emacs keybinding mode
+  extensions: [],               // additional CodeMirror extensions
+  onChange: (value) => {},       // called on content change
+})
+```
+
+## Languages
+
+20+ languages, lazy-loaded on demand — zero cost until used:
+
+```tsx
+editor.language.set('typescript')  // switch language dynamically
+```
+
+Supported: `javascript`, `typescript`, `jsx`, `tsx`, `html`, `css`, `json`, `markdown`, `python`, `rust`, `sql`, `xml`, `yaml`, `cpp`, `java`, `go`, `php`, `ruby`, `shell`, `plain`
+
+```tsx
+import { getAvailableLanguages, loadLanguage } from '@pyreon/code'
+
+getAvailableLanguages()           // list all supported
+await loadLanguage('typescript')  // preload a language
+```
+
+## Themes
+
+```tsx
+import { lightTheme, darkTheme, resolveTheme } from '@pyreon/code'
+
+// Switch dynamically
+editor.theme.set('dark')
+editor.theme.set('light')
+
+// Custom theme — pass any CodeMirror theme Extension
+editor.theme.set(myCustomTheme)
+```
+
+## Actions
+
+```tsx
+editor.focus()                           // focus the editor
+editor.insert('// comment')             // insert at cursor
+editor.replaceSelection('replacement')   // replace selected text
+editor.select(0, 10)                     // select range
+editor.selectAll()                       // select all
+editor.goToLine(42)                      // jump to line
+editor.undo()                            // undo
+editor.redo()                            // redo
+editor.foldAll()                         // fold all code blocks
+editor.unfoldAll()                       // unfold all
+editor.scrollTo(position)               // scroll to character position
+```
+
+## Diagnostics (Lint Integration)
+
+Push diagnostics from external tools (TypeScript, ESLint, etc.):
+
+```tsx
+editor.setDiagnostics([
+  { from: 0, to: 5, severity: 'error', message: 'Unexpected token', source: 'typescript' },
+  { from: 20, to: 30, severity: 'warning', message: 'Unused variable', source: 'eslint' },
+])
+
+editor.clearDiagnostics()
+```
+
+Severities: `'error'` | `'warning'` | `'info'` | `'hint'`
+
+## Line Highlights
+
+Highlight specific lines (errors, breakpoints, current execution):
+
+```tsx
+editor.highlightLine(5, 'error-line')      // add highlight
+editor.highlightLine(10, 'current-line')   // different style
+editor.clearLineHighlights()                // remove all
+```
+
+## Gutter Markers
+
+Add icons in the gutter (breakpoints, error indicators):
+
+```tsx
+editor.setGutterMarker(5, { text: '🔴', title: 'Breakpoint' })
+editor.setGutterMarker(12, { text: '⚠️', title: 'Warning', class: 'warning-marker' })
+editor.clearGutterMarkers()
+```
+
+## Custom Keybindings
+
+```tsx
+editor.addKeybinding('Ctrl-Shift-L', () => {
+  console.log('Custom shortcut!')
+  return true
+})
+```
+
+## Text Queries
+
+```tsx
+editor.getLine(5)          // text of line 5
+editor.getWordAtCursor()   // word under cursor
+```
+
+## Minimap
+
+Canvas-based code overview with viewport indicator and click-to-scroll:
+
+```tsx
+const editor = createEditor({
+  value: longCode,
+  minimap: true,  // enable minimap
+})
+```
+
+The minimap renders a scaled-down view of the entire document on the right side. Click to jump to that section. The viewport rectangle shows your current position.
+
+## Diff Editor
+
+Side-by-side or inline diff using `@codemirror/merge`:
+
+```tsx
+import { DiffEditor } from '@pyreon/code'
+
+<DiffEditor
+  original="const x = 1\nconst y = 2"
+  modified="const x = 1\nconst y = 3\nconst z = 4"
+  language="typescript"
+  theme="dark"
+  style="height: 400px"
+/>
+
+// Inline diff
+<DiffEditor original={old} modified={new} inline />
+
+// Reactive — pass signals
+<DiffEditor original={originalSignal} modified={modifiedSignal} />
+```
+
+## Tabbed Editor
+
+Multi-file editing with tab management:
+
+```tsx
+import { createTabbedEditor, TabbedEditor } from '@pyreon/code'
+
+const editor = createTabbedEditor({
+  tabs: [
+    { name: 'index.ts', language: 'typescript', value: 'const x = 1' },
+    { name: 'style.css', language: 'css', value: '.app { color: red; }' },
+    { name: 'data.json', language: 'json', value: '{ "key": "value" }' },
+  ],
+  theme: 'dark',
+})
+
+<TabbedEditor instance={editor} style="height: 500px" />
+```
+
+### Tab Operations
+
+```tsx
+editor.tabs()               // Signal<Tab[]> — all open tabs
+editor.activeTab()          // Computed<Tab | null> — current tab
+editor.activeTabId()        // Signal<string>
+
+// Lifecycle
+editor.openTab({ name: 'utils.ts', language: 'typescript', value: '' })
+editor.closeTab('style.css')
+editor.switchTab('index.ts')
+
+// Management
+editor.renameTab('index.ts', 'main.ts')
+editor.setModified('index.ts', true)    // show modified indicator
+editor.moveTab(0, 2)                     // reorder
+editor.closeAll()                        // close all closable tabs
+editor.closeOthers('index.ts')           // close all except one
+editor.getTab('index.ts')                // get tab by id
+```
+
+### Tab Features
+
+- **Modified indicator** — dot shown on tabs with unsaved changes
+- **Closable tabs** — set `closable: false` for pinned tabs
+- **Content preservation** — content cached when switching tabs
+- **Auto-switch** — closing active tab switches to adjacent
+
+## Vim / Emacs Mode
+
+Optional key modes (requires installing the package):
+
+```bash
+bun add @replit/codemirror-vim    # for vim mode
+bun add @replit/codemirror-emacs  # for emacs mode
+```
+
+```tsx
+const editor = createEditor({
+  value: 'hello world',
+  vim: true,   // enable vim mode
+})
+```
+
+## Accessing CodeMirror Directly
+
+For advanced use cases, access the underlying EditorView:
+
+```tsx
+const view = editor.view()  // EditorView | null (null before mount)
+
+if (view) {
+  // Use any CodeMirror API directly
+  view.dispatch({ ... })
+}
+```
+
+## API Reference
+
+### createEditor
+
+| Property | Type | Description |
+|---|---|---|
+| `value` | `Signal<string>` | Editor content — reactive |
+| `language` | `Signal<EditorLanguage>` | Current language |
+| `theme` | `Signal<EditorTheme>` | Current theme |
+| `readOnly` | `Signal<boolean>` | Read-only state |
+| `cursor` | `Computed<{line, col}>` | Cursor position |
+| `selection` | `Computed<{from, to, text}>` | Current selection |
+| `lineCount` | `Computed<number>` | Number of lines |
+| `focused` | `Signal<boolean>` | Focus state |
+| `view` | `Signal<EditorView \| null>` | CodeMirror instance |
+
+### createTabbedEditor
+
+| Method | Description |
+|---|---|
+| `openTab(tab)` | Open or switch to a tab |
+| `closeTab(id)` | Close a tab |
+| `switchTab(id)` | Switch to a tab |
+| `renameTab(id, name)` | Rename a tab |
+| `setModified(id, bool)` | Mark modified |
+| `moveTab(from, to)` | Reorder tabs |
+| `closeAll()` | Close all closable tabs |
+| `closeOthers(id)` | Close all except one |
+
+### Components
+
+| Component | Description |
+|---|---|
+| `<CodeEditor>` | Single-file editor |
+| `<DiffEditor>` | Side-by-side or inline diff |
+| `<TabbedEditor>` | Multi-file with tab bar |