ci(street-level): run the browser gate hermetically with Mapillary fixtures

The Street Level and panel gates never ran in CI, and the live gate needs a
Mapillary token, the Mapillary network and real coverage at its test site,
so everything users see was guarded only by manual runs (which a bad token
and expired tile caches blocked twice this week).

`qa-street-level.mjs --fixtures` (npm run qa:street-level:fixtures) answers
the page's /api/mapillary/status and coverage-tile requests from generated
tiles (a street grid with flat and 360 deg sequences, half captured three
years ago; overview points from orbit) and blocks mapillary.com. Only the
six steps that open a photo are skipped. Because the data is known, the 360
deg and SINCE steps also assert that the filters remove sequences, not just
that counts do not grow. A unit test pins the fixture contents.

New CI job "Street Level browser gate": install with headless Chrome, start
a key-less dev server, run the fixture gate and qa:panel-resize. Locally,
against a dev server with every key blanked: 14/14 on three consecutive
runs, panel gate all pass.

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

src/tooling/streetLevelQa.test.mjs

@@ -2,6 +2,7 @@ import assert from 'node:assert/strict';
 import fs from 'node:fs';
 import test from 'node:test';
 import {
+  fixtureTile,
   EXPECTED_PROVIDERS,
   isCollapsed,
   RAIL_ORDER,
@@ -44,3 +45,27 @@ test('the harness only runs its browser flow when executed directly', () => {
   assert.match(source, /PUPPETEER_EXECUTABLE_PATH/);
   assert.match(source, /--url/);
 });
+
+test('fixture tiles give the hermetic gate something real to filter', async () => {
+  const { decodeCoverageTile } =
+    await import('../layers/streetLevel/providers/mapillary/decode.js');
+  const now = Date.UTC(2026, 9, 1);
+  const street = decodeCoverageTile(fixtureTile(14, 2662, 6286, now), {
+    x: 2662,
+    y: 6286,
+    z: 14,
+  });
+  assert.equal(street.sequences.length, 8);
+  const pano = street.sequences.filter((s) => s.isPano).length;
+  assert.ok(pano > 0 && pano < 8, '360° and flat both present');
+  const year = 365 * 86_400_000;
+  const old = street.sequences.filter((s) => now - s.capturedAt > year).length;
+  assert.ok(old > 0 && old < 8, 'recent and older both present');
+  const orbit = decodeCoverageTile(fixtureTile(3, 1, 3, now), {
+    x: 1,
+    y: 3,
+    z: 3,
+  });
+  assert.ok(orbit.overview.length > 0, 'overview points from orbit');
+  assert.equal(fixtureTile(8, 1, 1, now).length, 0, 'nothing in between');
+});