Add explicit detectors and optional auth

docs/README.md

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+# face-lock docs
+
+## Overview
+
+face-lock is a FastAPI service that detects a primary subject, makes a square crop, and returns both a crop and an annotated preview.
+
+## Endpoints
+
+- `GET /health`
+- `GET /`
+- `POST /api/focus`
+- `POST /api/focus/image`
+- `GET /docs`
+
+## Detectors
+
+- `face` for human faces
+- `animal` for pets / animals, with a contour fallback
+- `person` for full-body person detection
+- `subject` for general foreground subjects
+
+## Authentication
+
+Set `FACE_LOCK_AUTH_TOKEN` to require a header token.
+
+Supported headers:
+
+- `X-API-Key: <token>`
+- `Authorization: Bearer <token>`
+
+Optional override:
+
+- `FACE_LOCK_AUTH_HEADER` changes the expected header name.
+
+## Example
+
+```bash
+curl -H 'X-API-Key: your-token' \
+  -F 'file=@image.jpg' \
+  -F 'detector=animal' \
+  http://localhost:8000/api/focus
+```