docs(phase-15): complete phase execution — verification passed

- VERIFICATION.md: 3/3 must-haves verified, 124/124 tests green
- ROADMAP.md: Phase 15 marked complete
- STATE.md: advanced to post-phase state

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

.planning/STATE.md

@@ -1,3 +1,19 @@
+---
+gsd_state_version: 1.0
+milestone: v1.1
+milestone_name: Hardening & Validation
+current_plan: 1
+status: completed
+stopped_at: Completed 15-ux-driver-upload-feedback-fix/15-01-PLAN.md
+last_updated: "2026-04-16T14:37:17.811Z"
+last_activity: 2026-04-16
+progress:
+  total_phases: 6
+  completed_phases: 6
+  total_plans: 21
+  completed_plans: 21
+---
+
 ---
 gsd_state_version: 1.0
 milestone: v1.1