fix(sidebar): expose the active nav destination to assistive tech

[pedrofrxncx]

Accessibility gap in the sidebar's destination list (Home / Reports / Tasks / Library, plus coding-agent rows): the active item is only marked via a data-active attribute used for CSS styling — nothing tells assistive tech which destination is currently selected.

Why it matters: a screen-reader user navigating this list has no way to tell which destination (or coding agent) is currently open; sighted users get this for free from the active-state styling.

Fix: add aria-current="page" on the active SidebarMenuButton, mirroring item.isActive (already computed for both destinations and coding-agent rows, since row() is shared). SidebarMenuButton (packages/ui) spreads unknown props onto the underlying element, so no change to the shared component was needed.

To confirm: open the sidebar, select a destination, and inspect the corresponding <button> — it now carries aria-current="page"; inactive rows have no aria-current attribute.

Checks run locally: bun run fmt, bunx tsc --noEmit (apps/web, clean), bunx oxlint apps/web/src/components/sidebar/nav-destinations.tsx (0 warnings/errors). No existing test covers this file (it's hook-heavy, not pure logic) — full CI validates the rest.

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Summary by cubic

Marks the active sidebar destination with aria-current="page" so screen readers can announce the current page. Previously only a data-active attribute indicated the active item; now the active button exposes its state without changing visuals.

• Applies to both standard destinations and coding-agent rows by mirroring item.isActive.
• Implemented by passing aria-current to SidebarMenuButton; packages/ui already forwards unknown props, so no shared UI change.
• Review: select a destination and inspect the button; it has aria-current="page". Inactive items have no aria-current.

^{Written for commit 4250a8a. Summary will update on new commits.}