feat(tui): add 9 user flow integration tests (bd-2ygk)

Implements end-to-end flow tests covering all PRD Section 6 journeys:
- Morning triage (dashboard -> issue list -> detail -> back)
- Direct screen jumps (g-prefix chain: gt -> gw -> gi -> gh)
- Quick search (g/ -> results -> drill-in -> back with preserved state)
- Sync and browse (gs -> sync lifecycle -> complete -> browse)
- Expert navigation (gw -> Who -> verify expert mode default)
- Command palette (Ctrl+P -> verify open/filtered -> Esc close)
- Timeline navigation (gt -> events -> drill-in -> back)
- Bootstrap sync flow (Bootstrap -> gs -> SyncCompleted -> Dashboard)
- MR drill-in and back (gm -> detail -> Esc -> cursor preserved)

Key testing patterns:
- State generation alignment for dual-guard stale detection
- Key event injection via send_key/send_go helpers
- Data injection via supervisor.submit() + Msg handlers
- Cross-screen state preservation assertions

.beads/last-touched

@@ -1 +1 @@
-bd-2nfs
+bd-2ygk