feat: upstream cookie proxy, HLS connection pool, multi-link TG notifications

- Add upstream Cookie support for HLS full-proxy mode (CloudFront signed cookies
  stored server-side as opaque tokens; never exposed in proxy URLs)
- Add HTTP connection pool for HLS proxy upstream requests to avoid per-request
  TLS handshake overhead; introduce HLS_PROXY_TIMEOUT separate from probe timeout
- Add per-link TG start notification with 30s merge window: each newly-live link
  fires independently, links that come online within the window are merged into
  one message with names joined by ' & '
- Fix TG reconnect grace period (TG_RECONNECT_GRACE_SECS=60): suppress both
  stop and start notifications for brief RTMP disconnects
- Fix stream probe to check all links for TG-enabled streams; non-TG streams
  still stop at first valid link to avoid unnecessary probes
- Filter high-frequency HTTP access log entries (HLS segments, heartbeat, etc.)
- Add json-file logging driver config to docker-compose for reliable log access

docker-compose.yml

@@ -22,6 +22,11 @@ services:
       - ./videos:/app/videos
       # Mount additional directories as needed:
       # - /local/path:/app/media/label
+    logging:
+      driver: json-file
+      options:
+        max-size: "10m"
+        max-file: "3"
 
   postgres:
     image: postgres:16-alpine