feat: add Errands nav item, /errands route, and CreateErrandDialog
- AppLayout: add Errands nav entry with pending_review badge count
- /errands route: list table with ID, description, branch, status, agent, created columns; empty state with CLI hint; slide-over integration
- CreateErrandDialog: description (max 200 chars with counter), project select, optional base branch; no optimistic UI due to agent spawn latency
- ErrandDetailPanel: checkout from completed dependency commit (4j3ZfR_ZX_4rw7j9uj6DV)
TypeScript compiles clean. Route uses TanStack Router file-based routing; routeTree.gen.ts auto-regenerated on build.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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