feat(street-level): IMAGERY and SINCE filters for KartaView

KartaView filters coverage on its server only in its PNG tiles (its JSON
tiles come back empty with a filter), so a filtered tile's PNG is a mask
over the cached JSON segments: a segment stays when at least half the
points along it lie on drawn pixels. A filter change reloads the lines
(lineCoverage.reload keeps the drawn ones until the new ones are in);
masks are cached per filter and tile, and a filtered tile KartaView is
still drawing (504 or a timeout) is asked again, four tries in all.
The nearest lookup asks the photo API for the projection and date, and
the cones follow the filter like Mapillary's. The gate fixture draws
filtered PNG tiles and adds an older flat-only street; a new gate step
checks 360 and LAST YEAR thin KartaView's lines and ALL brings them back.

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

CHANGELOG.md

@@ -114,7 +114,11 @@
   answers 409) are skipped by the click and by ‹ ›. Shift+← →, ↑ ↓, + − and
   pinch look around a 360° photo. The open photo's marker is a purple view
   cone pointing along the drive (KartaView's own compass headings are often
-  0 or far off).
+  0 or far off). The IMAGERY (ALL / 360° / FLAT) and SINCE filters apply to
+  KartaView as to Mapillary: its lines are filtered by KartaView's own
+  server (its filtered PNG tiles, as a mask over the JSON lines; SINCE goes
+  by upload date there), and the photo a click opens, and the cones, by
+  each photo's projection and capture date.
   Mapillary's line coverage and sequence cones are now shared by both
   (`lineCoverage.js`, `sequenceCones.js`).