feat: single-checkout local mode with refresh, nav project search

[flexdinesh]

• Behavior owner and resulting change:
  • contextservice: new Scope policy (checkout keys, or piped submission) applied to list/count/get/resolve/delete; composed by daemon from the initial request → local process only shows its own checkout/capture, others 404.
  • serverapp: Options.Collect → POST /api/v2/collections (registered only when present), local bootstrap collect; bare /mcp follows newest collection. cmd/diffx supplies the closure for worktree input only.
  • Web: header shows static repo/branch/worktree (picker trigger removed; dialog via Cmd/Ctrl+K or nav "Browse all reviews"); projects nav gets inline "Search projects" filter; Refresh/Alt+R collect checkout and open new snapshot; collapsed diff files + closed folders persist in sessionStorage.
• Contracts/invariants affected; local/remote implications:
  • OpenAPI: new collectCheckout route, required collect on local bootstrap. Remote unchanged (no scope, no route).
  • Snapshot diff.refresh still unavailable for stored observations; collection creates new observations. Failed collection → 422, nothing ingested. Explicit refresh may replace open review; arrivals still never do.
• Validation results; remaining risks:
  • mise run check passes (Go incl. conformance + race-free boundary tests, contracts, web 53 unit / 77 browser, plugins); embedded dist clean.
  • New tests: scope (contextservice), collection route/bootstrap/MCP pin (serverapp), conformance for checkout refresh + per-process isolation + piped 404, browser tests for nav search, refresh, collapse persistence.
  • Risks: in-scope expired context delete now 404 vs prior delete; out-of-scope expired reads report 410 (expiry checked first); collection mutex not request-cancellable.
• Intentional architecture/design changes and rationale:
  • Local mode is explicitly single-checkout: shared home DB retained every run, so the UI showed unrelated checkouts. Local collection now "at start and on explicit request" (docs/architecture.md, system.md, development.md, README, DESIGN.md updated).
• UI evidence: header identity height/icon sizes asserted against existing controls; nav search uses file-filter search-box primitive; mobile drawer density test updated; keyboard: Escape clears nav search, Cmd/Ctrl+K picker, Alt+R refresh.