- Layer 2 fallback: user tags overlapping with auto-tag categories
(HIGH/LOW/I2V/T2V/TI2V/Lightning/Turbo) are merged into auto_tags,
providing manual override when filename-based detection fails.
Matching is case-insensitive so "high"/"High"/"HIGH" all work.
- Refresh on tag edit: save_metadata and add_tags handlers now return
recalculated auto_tags in the response; the frontend passes them to
VirtualScroller.updateSingleItem so badges update immediately without
requiring a page reload.
- 8 new test cases for Layer 2 fallback and case-insensitive matching.