feat(media): Make variant generation atomic with database

Per v1.5.0 Phase 4:
- Generate variants to temp directory first
- Perform database inserts in transaction
- Move files to final location before commit
- Clean up temp files on any failure
- Add startup recovery for orphaned temp files
- All media operations now fully atomic

Changes:
- Modified generate_all_variants() to return file moves
- Modified save_media() to handle full atomic operation
- Add cleanup_orphaned_temp_files() for startup recovery
- Added 4 new tests for atomic behavior
- Fixed HEIC variant format detection
- Updated variant failure test for atomic behavior

Fixes:
- No orphaned files on database failures
- No orphaned DB records on file failures
- Startup recovery detects and cleans orphans

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

starpunk/__init__.py

@@ -128,9 +128,12 @@ def create_app(config=None):
     configure_logging(app)
 
     # Clean up old debug files (v1.5.0 Phase 2)
-    from starpunk.media import cleanup_old_debug_files
+    from starpunk.media import cleanup_old_debug_files, cleanup_orphaned_temp_files
     cleanup_old_debug_files(app)
 
+    # Clean up orphaned temp files (v1.5.0 Phase 4)
+    cleanup_orphaned_temp_files(app)
+
     # Initialize database schema
     from starpunk.database import init_db, init_pool