Validate provider response formats

CCTV frames and the Street View fallback accept only JPEG, PNG, GIF, WebP and
AVIF, parsed from the media type essence and sent under the canonical type;
any other type is cancelled and falls through to the next fallback as a
failed upstream does. Live media must match its feed kind (video/mp4,
video/webm, or multipart/x-mixed-replace with a boundary) before the camera
is reported healthy or any byte is relayed, and its redirects now stay on the
registered origin like frames. Every /api/cctv route uses the same-site gate.

The GBFS proxy relays only bodies that parse as JSON, re-serialized under a
fixed application/json type.

scripts/package-boundaries.json

@@ -194,6 +194,8 @@
     "exports": ["./server/providers/cctv"],
     "modules": [
       "server/providers/cctv.js",
+      "server/providers/common/same-site.js",
+      "src/localRequestGate.mjs",
       "server/providers/cctv/cap.js",
       "server/providers/cctv/groundHeights.js",
       "server/providers/cctv/catalog.js",