fix(tools): identify historical camera fallback imagery (#1118)

The CCTV frame proxy marks a Street View fallback with X-CCTV-Source, but the portable source dropped the header and get_cctv_snapshot always reported a current view credited to the camera's agency. The source now keeps the recognised provenance, and the tool labels Street View frames as historical Google imagery, refuses synthetic placeholders, and reports unknown provenance without claiming a current view.

docs/CURRENT-STATE.md

@@ -1370,6 +1370,14 @@ outside its promise, so an unusual mirror status cannot crash the server.
 Node-only package entries expose both provider factories. Routes, payloads,
 fallback behavior and existing dev/preview hook registration are preserved;
 browser rendering is unchanged.
+The portable frame source retains the proxy's known `X-CCTV-Source` kind. Camera
+snapshot tools label Street View fallback imagery as historical and credit Google,
+while upstream frames retain their current-view label and catalog attribution.
+Synthetic placeholders are unavailable as snapshots. Injected frame sources may
+supply `sourceKind`; missing or unknown provenance keeps `current_view` null and
+does not claim the image is current. The `current_view` field distinguishes camera-feed
+provenance from historical fallback imagery; it does not measure capture time or
+image freshness.
 
 ## CCTV missing numeric fields