docs(21-03): complete cross-screen navigation & mobile responsive plan

Tasks completed: 2/2
- Add cross-screen navigation links
- Fix mobile responsive layout for detail panels

SUMMARY: .planning/phases/21-polish-integration/21-03-SUMMARY.md

.planning/STATE.md

@@ -9,10 +9,10 @@ See: .planning/PROJECT.md (updated 2026-02-04)
 
 ## Current Position
 
-Phase: 20 of 21 (Real-Time Subscriptions) - COMPLETE
-Plan: 2 of 2 in current phase (all complete)
-Status: Completed 20-02 (Frontend SSE Subscription Hooks)
-Last activity: 2026-02-04 - Completed 20-02-PLAN.md (frontend subscriptions)
+Phase: 21 of 21 (Polish & Integration) - In progress
+Plan: 3 of 6 in current phase
+Status: Completed 21-03 (Cross-Screen Navigation & Mobile Responsive)
+Last activity: 2026-02-05 - Completed 21-03-PLAN.md (navigation links + mobile responsive)
 
 Progress: █████████░ 99%
 
@@ -233,6 +233,10 @@ Recent decisions affecting current work:
 - 20-02: Subscription-driven invalidation (not local state) — simplest approach, reuses existing React Query cache
 - 20-02: Silent onError callbacks — pages degrade to manual refresh when backend is not running
 - 20-02: No new packages needed — splitLink and httpSubscriptionLink ship with @trpc/client v11
+- 21-03: Removed disabled nav stubs (Agents, Tasks, Settings) — stubs create false promises for v2.0
+- 21-03: TaskRow agent names link to /inbox — simplest cross-screen navigation for agent context
+- 21-03: Inbox task links go to /initiatives — no direct task-to-initiative mapping on frontend
+- 21-03: Mobile drill-down pattern hides list on mobile when detail selected, shows back button
 
 ### Pending Todos
 
@@ -254,6 +258,6 @@ None.
 
 ## Session Continuity
 
-Last session: 2026-02-04
-Stopped at: Completed 20-02 (Frontend SSE Subscription Hooks) — Phase 20 complete
+Last session: 2026-02-05
+Stopped at: Completed 21-03 (Cross-Screen Navigation & Mobile Responsive)
 Resume file: None