fix: stale frigate mapping reconciliation, recognize opt-out, cold start notice

- At upload start, diff tracker vs live Frigate file list and remove any
  mappings for files no longer present; corrects effective_count so manually
  deleted files don't permanently consume quota slots
- Add ENABLE_FRIGATE_SCORES config (default true); when false, skips all
  recognize_face calls and falls back to blur scores for quality replacement
- Print a dim notice when FRIGATE_SCORE_THRESHOLD is set but pre_run_count
  is zero, so users know the gate is deferred to the next run

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -31,6 +31,7 @@ STRATEGY=auto
 # BLUR_THRESHOLD=120.0        # Laplacian blur threshold; lower = accept more blur (default: 120.0)
 # MAX_AUTO_IMAGES=80          # Hard cap on auto-diversity selection (default: 80)
 # FRIGATE_SCORE_THRESHOLD=0.0 # Quality gate: remove images scoring below this after upload (0 = disabled; requires at least one prior run)
+# ENABLE_FRIGATE_SCORES=true  # Call Frigate's recognize endpoint after each upload to store quality scores (default: true; adds ~200ms per upload)
 
 # ── Caching & Models ──────────────────────────────────────────────────────────
 # FORCE_CPU=true              # Disable GPU, fall back to CPU