refactor(street-level): trim QA, tests, styles and docs

The browser gate is one pass over the remaining flows: rail strip and
expand, coverage with fixtures, the ON/OFF pill, 360° and SINCE filters,
KEY REJECTED, nearest photo with caption, × close, phone fit, keyless
KEY REQUIRED on a second page and no page errors. Panel controls are
pressed through the DOM; pick-point search, line/cone clicks, the
framing-cancel, reload/share and status-route probes, the second
viewport and pointer-settling retries are gone (unit tests cover them).

Tests that pinned constants, copy, CSS or source text, or repeated
another test, are removed or merged. CSS loses an unused variable and
duplicate rules. Docs describe the slimmed feature; unused exports and
the layer's dead setCoverageFilter/refreshCoverage surface are removed.

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

docs/CURRENT-STATE.md

@@ -2934,58 +2934,44 @@ its criteria cannot be silently ignored.
 
 Fire Perimeters uses capped, timed server reads with stale-on-error caching and a per-client limit. Unchanged snapshots retain geometry; link checks cancel on disable or selection change, and the row legend shows reported containment.
 
-Street Level is a collapsible right-rail panel (`#street-level-panel`, layer
-token `0`, option owner `street-level`, panel `ui` token `t`) that starts
+Street Level is a docked, collapsible right-rail panel (`#street-level-panel`,
+layer token `0`, option owner `street-level`, panel `ui` token `t`) that starts
 collapsed. It opens itself only when the user, voice or a tool switches the
 layer on or a photo opens, never on a restore, and those opens are not stored.
-Like the iD editor's photo overlay, it shows Mapillary with 360°/flat and
+Like the iD editor's photo overlay it shows Mapillary only: 360°/flat and
 captured-since filters (relative days, so a link keeps its meaning), one
-viewer host and an on-globe credit while the layer is on. Lines and cones are
-Mapillary green; 360° cones are rings and the selected sequence is GEV cyan.
-Share options: `m` (Mapillary on/off; off draws nothing), `p` (`a`/`p`/`f`
-panoramas), `s` (since, days). Without `MAPILLARY_CLIENT_TOKEN` the panel
-reads KEY REQUIRED, its error line says which key to add, and the filters are
-disabled. Coverage is z11–14 sequence lines below 60 km; above that nothing is
-drawn and the panel says to zoom in. Tiles come from the visible ground within
-range of the camera (rays meet the terrain height, not the bare ellipsoid),
-nearest the camera first, at most 9. The proxy serves only z11–14, strips the
-unused `image` layer from z14 tiles (12 MB → ~80 KB) and shares one upstream
-fetch between concurrent requests for a tile. A 429 pauses tile requests for
-its Retry-After and then refreshes once; a rejected key stops them and reads
-KEY REJECTED until the layer goes off.
+embedded viewer and an on-globe credit while the layer is on. Share options:
+`m` (Mapillary on/off; off draws nothing), `p` (`a`/`p`/`f` panoramas), `s`
+(since, days). The header pill is the only layer switch and also turns a
+switched-off `m` back on.
 
-Sequence lines are `GroundPolylinePrimitive`s with
-`ClassificationType.BOTH`, so they drape on the terrain globe and on Google 3D
-tiles alike (on 3D tiles they can land on roofs and tree tops). Cones and the
-photo marker are billboards clamped to the ground; they skip the depth test, so
-a horizon cull hides the ones behind the globe. Roads on elevated decks are
-drawn at ground level.
+Coverage is z11–14 sequence lines below 60 km; above that nothing is drawn and
+the panel says to zoom in. Tiles come from the visible ground within range of
+the camera, nearest first, at most 9. Lines are draped
+`GroundPolylinePrimitive`s (`ClassificationType.BOTH`), so they follow terrain
+and Google 3D tiles alike; cones and the photo marker are ground-clamped
+billboards with a horizon cull. Without `MAPILLARY_CLIENT_TOKEN` the panel
+reads KEY REQUIRED, says which key to add and disables the filters; a rejected
+key reads KEY REJECTED and stops tile requests until the layer goes off; a 429
+pauses them for its Retry-After.
 
-The header pill is the only layer switch; switching on also turns Mapillary
-back on if a share link or tool switched it off. The viewer sits under the header
-with EXPAND, FIT/FILL and close above the image. EXPAND is the browser's
-Fullscreen API on the viewer element, which stays in the panel (Esc or SHRINK
-leaves; the button is hidden where the API is missing). MapillaryJS loads on the
-first photo (no prewarm). Opening a photo flies the globe camera once to frame
-it; there is no camera follow. The flight goes
-through the application's deferred navigation (`attachNavigation`: `begin` /
-`reassert`), which releases aircraft and satellite tracking and is refused in
-the cockpit; a photo takes its ticket when it starts opening and frames only
-if nothing newer took the camera while it loaded. SINCE is a stepped slider whose readout names the
-cut-off date. At phone width (≤720 px) the viewer height is derived from the
-rail band so the whole photo fits.
+The server proxy (`server/providers/mapillary.js`) keeps the token server-side,
+serves only z11–14 coverage, strips the unused `image` layer, coalesces
+concurrent requests and keeps tiles in a 24 h memory cache.
 
-The layer (`src/layers/streetLevel/index.js`) owns the Mapillary parts
-directly: `providers/mapillary/` holds the source, tile decoding, coverage,
-sequence cones, nearest-image lookup and the MapillaryJS viewer.
+MapillaryJS loads on the first photo. Opening one frames it with a single
+camera flight through the application's deferred navigation (`begin` /
+`reassert`): it releases tracking, is refused in the cockpit, and is skipped
+if newer navigation took the camera while the photo loaded; closing the photo
+cancels it. EXPAND is the browser's Fullscreen API on the viewer element
+(hidden where the API is missing). At phone width the viewer height comes from
+the rail band so the whole photo fits.
 
-Street Level has two browser gates. `npm run qa:street-level -- --url <server>`
-runs against real Mapillary and needs `MAPILLARY_CLIENT_TOKEN`. `npm run
-qa:street-level:fixtures -- --url <server>` answers every Mapillary request
-from fixtures (`providers/mapillary/coverageFixture.mjs`,
-`scripts/fixtures/street-level/`), so it needs no network and covers the whole
-photo flow. CI runs the fixture gate against a production build served by
-`vite preview` with a dummy token.
+Browser gates: `npm run qa:street-level -- --url <server>` runs against real
+Mapillary with a token; `npm run qa:street-level:fixtures` answers every
+Mapillary request from fixtures (`providers/mapillary/coverageFixture.mjs`,
+`scripts/fixtures/street-level/`). CI runs the fixture gate with `--strict`
+against a production build served by `vite preview` with a dummy token.
 
 Directions is a keyless front end to the routing the voice agent already
 uses. Its row chips are the whole interface: DRIVE / WALK / BIKE pick the