feat: add vision pipeline scaffolding with ONNX backend

Introduce the app/services/vision/ module with ABC interfaces, ONNX
Runtime backend, model registry, and per-task implementations:
- OpenCLIP ViT-B/32 embedder (image + text, 512-d)
- RapidOCR engine (PP-OCRv4 via ONNX, no PaddlePaddle)
- YOLOv8n object detector (raw ONNX, no ultralytics runtime)
- YuNet + SFace face processor (Apache 2.0, opencv_zoo, 128-d)
- DBSCAN face clustering helper

Add VisionSettings to config (mulita.yml + Pydantic), bootstrap_models.py
for first-boot weight downloads, models_data Docker volume, and ROCm
backend stub for future GPU acceleration.

No Celery tasks wired yet — models load but nothing invokes them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -69,6 +69,7 @@ services:
       - thumbs_data:/data/thumbs
       - proxies_data:/data/proxies
       - db_data:/data/db
+      - models_data:/data/models
     environment:
       - DATABASE_URL=postgresql+asyncpg://mulita:mulita@db:5432/mulita
       - REDIS_URL=redis://redis:6379
@@ -130,4 +131,5 @@ volumes:
   proxies_data:
   db_data:
   redis_data:
-  pg_data:
+  pg_data:
+  models_data: