docs: mark Phase 6 and milestone complete

All 6 phases of multi-provider support milestone finished:
- Phase 1: Provider Infrastructure
- Phase 2: Model Discovery
- Phase 3: Generate Node Refactor
- Phase 4: Model Search Dialog
- Phase 5: Image URL Server
- Phase 6: Video & Polish

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -19,7 +19,7 @@ None
 - [x] **Phase 3: Generate Node Refactor** - Rename NanoBanana to generic Generate with multi-model support ✓
 - [x] **Phase 4: Model Search Dialog** - Floating action bar icons and searchable model browser ✓
 - [x] **Phase 5: Image URL Server** - Local endpoint serving images as URLs for providers ✓
-- [ ] **Phase 6: Video & Polish** - Video playback, parameter customization, edge cases (In progress)
+- [x] **Phase 6: Video & Polish** - Video playback, parameter customization, edge cases ✓
 
 ## Phase Details
 
@@ -87,7 +87,7 @@ Plans:
 - [x] 06-01: GenerateVideo node with video-capable model selector
 - [x] 06-02: Video playback in output node
 - [x] 06-03: Custom model parameters from provider schemas
-- [ ] 06-04: Edge case handling and final polish
+- [x] 06-04: Edge case handling and final polish
 
 ## Progress
 
@@ -101,4 +101,4 @@ Phases execute in numeric order: 1 → 2 → 3 → 4 → 5 → 6
 | 3. Generate Node Refactor | 3/3 | Complete | 2026-01-09 |
 | 4. Model Search Dialog | 2/2 | Complete | 2026-01-09 |
 | 5. Image URL Server | 2/2 | Complete | 2026-01-09 |
-| 6. Video & Polish | 3/4 | In progress | - |
+| 6. Video & Polish | 4/4 | Complete | 2026-01-11 |