feat(team-inbox): add unified team inbox

[beruro]

Summary

• add a viewer-scoped SQLite projection for assigned Work Items with stable cursor pagination and durable read receipts
• merge local assignments with Zod-validated managed-cloud comment mentions behind one Team Inbox data source
• add the Team Inbox master/detail surface, unread badge, read/unread actions, filtering, search, pagination, and canonical Session / Work Item navigation
• wire a singleton Chat Panel tab and the current modular develop Sidebar without carrying over the old monolithic connector implementation

Validation

• pnpm exec tsc --noEmit --pretty false
• eslint on every changed TypeScript/TSX file
• focused Vitest suite: 86 tests passed
• cargo test --manifest-path src-tauri/Cargo.toml -p project_management team_inbox --no-fail-fast: 12 passed
• cargo check --manifest-path src-tauri/Cargo.toml -p org2
• git diff --check

Audits

• Architecture: all 10 layers covered; explicit viewer IDs, tagged DTOs, command-registration parity, and canonical schema initialization verified.
• Frontend UI: 7 fixes applied, 4 patterns kept with documented reasons, 0 remaining abstraction candidates.
• Performance: pass. No timer or polling loop; refresh is demand/signal driven, concurrent list reads are single-flight, stale loads are generation-guarded, and cloud read receipts are capped at 1,000 entries.

Detailed reports are included under docs/architecture-audit-2026-07-23/TeamInbox.md and docs/frontend-ui-audit-2026-07-23/TeamInbox.md.