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/TOOLS.md

@@ -273,7 +273,7 @@ and the development server's internal routes. See SECURITY.md.
 | `next_satellite_pass` | `satellites` | Next pass over a place or point (default the ISS), with naked-eye visibility |
 | `satellites_overhead` | `satellites` | Satellites in a CelesTrak group above a place or point now, highest first |
 | `find_cctv_cameras` | `cctv` | Public cameras in an area, nearest first |
-| `get_cctv_snapshot` | `cctv` | The current image from one camera, returned as image content |
+| `get_cctv_snapshot` | `cctv` | An image from one camera, returned as image content; Street View fallbacks are labelled historical |
 | `find_alpr_cameras` | `alpr` | OpenStreetMap-mapped license plate readers in a US/Canadian area up to 3° |
 | `find_radio_stations` | `radio` | Radio Browser stations by area and/or search terms, with stream URLs |
 | `search_places` | `placeSearch` | Points of interest matching a query within an area (Google Places) |