Changes:
1. helpers.py (_track_image_operation_usage): Map provider name to DB columns
dynamically (stability→stability_calls, wavespeed→wavespeed_calls, etc.)
instead of hardcoding stability_calls/stability_cost.
2. upscale_service.py: Added _track_image_operation_usage() call after
successful Stability upscale completion.
3. control_service.py: Added _track_image_operation_usage() call after
successful Stability control operation completion.
4. edit_service.py: Added _track_image_operation_usage() call after
successful Stability edit operation (remove_background, inpaint,
outpaint, search_replace, search_recolor, relight).
Previously only Create Studio and Face Swap tracked usage. Now all five
studios correctly decrement subscription limits.
- Added new router for content assets
- Added new service for content assets
- Added new model for content assets
- Added new utils for content assets
- Added new docs for content assets
- Added new tests for content assets
- Added new examples for content assets
- Added new guides for content assets
