docs(04-01): complete plan summary, update STATE, clean handoff

Plan 04-01 (marketplace browse + activate) done — 3 tasks, 9 tests,
10 files. Remove HANDOFF.json and .continue-here.md, advance to 04-02.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/STATE.md

@@ -5,7 +5,7 @@ milestone_name: milestone
 status: executing
 stopped_at: Phase 4 UI-SPEC approved
 last_updated: "2026-06-22T12:42:52.447Z"
-last_activity: 2026-06-22 -- Phase 04 execution started
+last_activity: 2026-06-23 -- Plan 04-01 completed
 progress:
   total_phases: 6
   completed_phases: 2
@@ -26,9 +26,9 @@ See: .planning/PROJECT.md (updated 2026-06-18)
 ## Current Position
 
 Phase: 04 (marketplace-portal-navigation) — EXECUTING
-Plan: 1 of 4
-Status: Executing Phase 04
-Last activity: 2026-06-22 -- Phase 04 execution started
+Plan: 2 of 4
+Status: Plan 04-01 complete, ready for 04-02
+Last activity: 2026-06-23 -- Plan 04-01 completed (marketplace browse + activate)
 
 Progress: [██▓░░░░░░░] 25%
 
@@ -93,6 +93,6 @@ Items acknowledged and carried forward from previous milestone close:
 
 ## Session Continuity
 
-Last session: 2026-06-22T11:55:16.369Z
-Stopped at: Phase 4 UI-SPEC approved
-Resume file: .planning/phases/04-marketplace-portal-navigation/04-UI-SPEC.md
+Last session: 2026-06-23T06:52:00Z
+Stopped at: Plan 04-01 complete, 04-02 ready
+Resume file: .planning/phases/04-marketplace-portal-navigation/04-02-PLAN.md