feat: add descriptive model naming and inline rename

- Auto-generate model names: {arch}-{labelType}-{epochs}ep-{classNames}-{YYYYMMDD}
- Add PATCH /api/models/{id}/rename endpoint
- Inline rename UI on Models & Training page
- Download filename uses model name instead of v{N}
- DB migration: add name column to model_versions
- Update all docs to reflect new naming convention

README.md

@@ -562,6 +562,7 @@ data/
     │   ├── images/{train,val}/             # Immutable frame images
     │   └── labels/{train,val}/             # YOLO format bounding box annotations (.txt)
     └── models/<n>/                         # Training runs (weights/best.pt, metrics.json, args.yaml)
+                                            # Named: {arch}-{labelType}-{epochs}ep-{classNames}-{date}
 ```
 
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