docs(18): create phase plan

.planning/STATE.md

@@ -4,8 +4,8 @@ milestone: v1.1
 milestone_name: Operability & Polish
 status: executing
 stopped_at: Phase 18 context gathered
-last_updated: "2026-06-15T01:25:46.051Z"
-last_activity: 2026-06-14
+last_updated: "2026-06-15T01:53:38.101Z"
+last_activity: 2026-06-15 -- Phase 18 planning complete
 progress:
   total_phases: 23
   completed_phases: 9
@@ -28,7 +28,7 @@ See: .planning/PROJECT.md (updated 2026-06-10)
 Phase: 13
 Plan: Not started
 Status: Ready to execute
-Last activity: 2026-06-14
+Last activity: 2026-06-15 -- Phase 18 planning complete
 
 ### ✅ Resolved Checkpoint — Phase 15 Plan 15-03 Task 2 (human-action)