feat(web): refine navigation and composer controls

[GCWing]

Summary

• Replace the top navigation voice action with a New session action and move realtime voice to a bottom-right Hello launcher.
• Add nested quick actions for appearance switching, ACP session creation, and additional composer modes.
• Simplify Harness, model, and reasoning controls while preserving additional modes as rich inline prompt references.
• Update focused tests and en-US, zh-CN, and zh-TW copy for the revised interactions.

Type and Areas

Type: Feature / UI/UX

Areas: Web UI, FlowChat, navigation, i18n

Motivation / Impact

This reduces top-level navigation and composer clutter while keeping advanced actions discoverable through grouped submenus. Session creation is promoted to the primary navigation utility area, realtime voice gains a dedicated launcher, and composer execution controls use a more compact hierarchy without losing prompt semantics.

Verification

• pnpm run check:web — passed, including Appearance, theme color, visual governance, and Web UI type checks.
• Focused Vitest run — 10 files and 87 tests passed.
• pnpm run i18n:audit — passed with 0 warnings.
• pnpm run motion:audit — inventory reviewed; the one reported reduced-motion item is an existing SSH dialog style outside this diff.
• git diff --check origin/1.0.0-explore...HEAD — passed.
• Browser/manual visual checks and E2E were not run; repository guidance asks to avoid browser-control validation and keep verification focused unless E2E is necessary.

Reviewer Notes

• AI-assisted change. Automated Web UI contracts and focused behavior tests were completed; no manual visual validation was performed.
• Remote scenario coverage: exercised only in the local Web UI test environment. Remote workspace, Remote Control, Peer Device Mode, and Detached Dispatch were not exercised. This PR does not change transport, protocol, persistence, or runtime ownership contracts.
• Temporary design/QA notes, homepage drafts, and NUL artifacts remain excluded from the branch.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.