Move InvSR download to runtime (avoids build OOM), add status endpoint

Pre-download SD-Turbo at build time, use snapshot_download for reliable caching

Add real InvSR model with CPU/float32 support (SD-Turbo + noise predictor)

Fix: switch to Python 3.12 for mewzoom compatibility

Add Super-Resolution API: MewZoom 2X/4X + comparison + metrics