Add label whitelist to filter detection types

DETECTION_LABELS env var accepts comma-separated list (e.g. "person,cat,dog").
Only matching detections are reported; others are ignored. Empty = report all.

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

server/env.example

@@ -60,6 +60,9 @@ DETECTION_CONFIDENCE=0.5
 # Set to false to keep reporting all motion events
 DETECTION_SUPPRESS_EMPTY=true
 
+# Only report these object types (comma-separated, empty = all)
+DETECTION_LABELS=person,cat,dog
+
 # ============ Event Collector ============
 
 # URL to POST motion events to (collector on Mac mini)