feat(cctv): add Houston TranStar camera pack

Register the keyless TranStar snapshot catalog as a live CCTV source,
synthesize frame URLs from validated numeric camera ids, and keep the
nearest cameras to Houston's metro cores under the existing catalog ceiling.

CHANGELOG.md

@@ -1,5 +1,16 @@
 # Changelog
 
+- Add Houston traffic cameras from Houston TranStar as a CCTV pack. The camera
+  list is one keyless JSON request to
+  `traffic.houstontranstar.org/data/layers/cctvSnapshots_json.js`; frames are
+  stills synthesized from each numeric camera id on `www.houstontranstar.org`,
+  so a catalog field cannot steer the proxy off-host. Cameras without a
+  snapshot id, and cameras outside Greater Houston, are dropped. By default
+  the 250 cameras nearest downtown, Uptown, the Medical Center, IAH and
+  Galveston load. `CCTV_HOUSTON_ENABLED=0` turns the pack off and
+  `CCTV_HOUSTON_MAX_SOURCES` changes the cap. The catalog-wide ceiling is
+  unchanged; extra cameras share it round-robin with the other packs.
+
 - The tracked-aircraft descriptor now publishes `verticalRateMps`, on both the
   civil and military layers, so a consumer reading `getTrackedInfo()` no longer
   has to reach past it into the raw poll record for climb/descent. Reported,