fix(street-level): bound the tile proxy's disk cache and keep tiles' age

From the IC8 review of #768 (P2s), each with a test that fails before:

- A tile read from disk keeps its real age in memory, and the trim rewrite
  keeps the file's mtime, so nothing is served past the 24 h TTL.
- The disk cache is swept in the background at most every 15 min: expired
  tiles go, then the oldest past 1 GiB. Coverage zooms the app never
  requests (z6-10) are refused with a 400, and layer names are matched as
  own keys only.
- The tests run against a temporary cache directory (a test seam) instead
  of writing into and deleting from the developer's real .gev-cache.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

CHANGELOG.md

@@ -17,6 +17,8 @@
 - Street Level loads the coverage you are looking at in tilted views. Tiles are ranked along the line of sight, from the ground under the camera to the ground at the centre of the screen, and screen rays meet the ground at its real height (Denver is 1,600 m up), so the streets in front of the camera are no longer dropped for tiles near the horizon. On Google 3D, lines that are placed on the bare earth no longer fall back to draping over roofs when their finer points cross grid cells the coarse ones skipped.
 - Street Level names a Mapillary token that Mapillary refuses: the panel reads KEY REJECTED and says to replace `MAPILLARY_CLIENT_TOKEN` in Provider Settings, instead of a raw "HTTP 403". The proxy stops asking Mapillary on every camera move after a refusal (for that token) or a rate limit (until its `Retry-After`), and the panel clears the message when the layer is switched off.
 
+- Street Level polish from review: whole-earth coverage dots on the far side of the globe no longer show through it; a 360° or flat filter keeps a dense tile's matching lines instead of losing them to the per-tile cap; lines that lost their ground heights are cast again rather than left draped; a selection made while lines rebuild is applied once they are ready; hovering picks at most every 120 ms; Esc shrinks the expanded viewer wherever focus is, and closing a photo leaves focus in the panel; switching the layer off and on during the first photo load no longer leaves the viewer stuck. Portable panels lift only after a real mouse or pen drag, never on a click or a touch swipe. The MapillaryJS stylesheet now loads with the viewer instead of on every page (about 85 KB less render-blocking CSS). The tile proxy's disk cache is swept of expired tiles and capped at 1 GiB, keeps a cached tile's real age in memory, and refuses zoom levels the app never requests.
+
 - Add Norway's road cameras from Statens vegvesen as a CCTV pack. The camera
   list is one keyless GeoJSON request to the agency's OGC API view of its
   DATEX 3.1 CCTV table, so no DATEX account is needed. Every working camera