refactor: strip AI pipeline to binary photo/other classifier

Drops face recognition, OCR, object detection, and semantic embeddings.
The sole remaining vision task is a CLIP-based binary classifier
(photography vs other); photos in "other" get needs_review=true so
screenshots, documents, memes and scans can be triaged from a new
filter pill in the UI.

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

backend/app/config.py

@@ -30,51 +30,16 @@ class PerformanceSettings(BaseModel):
     db_pool_max_overflow: int = 10
     db_pool_recycle: int = 3600
 
-class EmbedderSettings(BaseModel):
-    """CLIP / SigLIP embedding model settings.
-    Supported: "openclip_vitb32" (512-d), "siglip2_vitb16" (768-d, default)."""
-    name: str = "openclip_vitb32"
-    batch_size: int = 8
-
-class OCRSettings(BaseModel):
-    """PaddleOCR / rapidocr settings"""
-    enabled: bool = True
-    languages: list[str] = ["en"]
-    min_confidence: float = 0.5
-
-class DetectorSettings(BaseModel):
-    """YOLOv8n object detection settings"""
-    enabled: bool = True
-    min_confidence: float = 0.35
-    max_detections: int = 50
-
-class FacesSettings(BaseModel):
-    """YuNet + SFace face detection/recognition settings"""
-    enabled: bool = True
-    min_face_size: int = 40
-    recognition_threshold: float = 0.65
-    cluster_eps: float = 0.5
-
 class ClassifierSettings(BaseModel):
-    """CLIP zero-shot content classification settings"""
-    enabled: bool = True
+    """Binary content classifier (photography vs other)."""
     min_confidence: float = 0.3
 
 class VisionSettings(BaseModel):
-    """AI vision pipeline settings. Disabled when running on SQLite
-    (pgvector is required for embedding storage)."""
+    """Vision pipeline — one binary classifier (photography vs other)."""
     enabled: bool = True
-    backend: str = "onnx"           # "onnx" | "rocm" (future)
+    backend: str = "onnx"
     models_dir: str = "/data/models"
-    # ONNX Runtime execution providers in priority order.
-    # Auto-detected at startup; falls back to CPU if GPU is unavailable.
-    # Options: "CUDAExecutionProvider", "ROCMExecutionProvider",
-    #          "OpenVINOExecutionProvider", "CPUExecutionProvider"
     execution_providers: list[str] = ["CPUExecutionProvider"]
-    embedder: EmbedderSettings = EmbedderSettings()
-    ocr: OCRSettings = OCRSettings()
-    detector: DetectorSettings = DetectorSettings()
-    faces: FacesSettings = FacesSettings()
     classifier: ClassifierSettings = ClassifierSettings()
     worker_concurrency: int = 2