refactor: rename CACHE_DIR → DATA_DIR, container path .if_cache → data (#21)

* refactor: rename CACHE_DIR to DATA_DIR, default path .if_cache → data

CACHE_DIR held both the embedding cache and the SQLite tracker DB, making
the name misleading. DATA_DIR is more accurate.

- Config reads DATA_DIR first; falls back to CACHE_DIR with a deprecation
  warning so existing setups don't break on upgrade
- Default local path: data (was .if_cache)
- Docker default path: /app/data (was /app/.if_cache)
- Internal references (embeddings.py, upload_tracker.py) updated to DATA_DIR
- compose.yml, .env.example, README, wiki, and changelog updated
- Version bumped to 0.5.1

* chore: update lockfile

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

compose.yml

@@ -37,7 +37,7 @@ services:
       # - FORCE_CPU=true              # Disable GPU, fall back to CPU
       # - OPENVINO_DEVICE=GPU         # Intel variant only: use Arc/iGPU instead of CPU (default: CPU)
       # - ENABLE_CACHE=false          # Disable embedding cache (default: true)
-      - CACHE_DIR=/app/.if_cache
+      - DATA_DIR=/app/data
       - INSIGHTFACE_HOME=/models/.insightface
 
       # ── Tracker overrides (one-shot, remove after use) ────────────────────
@@ -57,7 +57,7 @@ services:
     volumes:
       # Replace with absolute paths on your host, e.g. /opt/winnow/models
       - /path/to/winnow/models:/models
-      - /path/to/winnow/cache:/app/.if_cache
+      - /path/to/winnow/data:/app/data
       - /path/to/winnow/output:/app/frigate_train
     restart: unless-stopped