feat: RGBA fix, per-person tracking, dry-run, retry-rejected, reset-person

- Fix RGBA→JPEG error: convert all images to RGB before saving
- Upload tracker: per-person breakdown in JSON, reset_person(), get_person_summary()
- mark_rejected() only fires on face-detection failures (not all HTTP 400s)
- New env vars: DRY_RUN, RETRY_REJECTED, RESET_PERSON
- Tracker summary printed at startup showing uploaded/rejected counts per person
- Document new env vars in compose.yml

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

compose.yml

@@ -18,6 +18,11 @@ services:
       # - SKIP_PEOPLE=Unknown
       # - MIN_FACE_COUNT=5
 
+      # ── Tracker overrides (one-shot, remove after use) ──
+      # - DRY_RUN=true           # Preview selection without downloading/uploading
+      # - RETRY_REJECTED=true    # Re-attempt previously rejected images
+      # - RESET_PERSON=John      # Clear uploaded+rejected history for one person
+
       # ── Scheduling ──
       # Cron expression (unset = run once and exit)
       - CRON_SCHEDULE=0 3 * * 0    # Every Sunday at 3 AM