feat(street-level): provider contract with Mapillary as the first provider

Street Level is now a provider-neutral layer modelled on the iD editor's
photo overlay. The core owns what every imagery provider shares: the
enable state and a switch per provider, the imagery filter (360°/flat and
captured-since in relative days), one click handler routed by pick prefix,
one viewer host that mounts whichever provider's viewer adapter owns the
open image, the position marker, camera follow, one on-globe credit per
active provider, and share-link parameters (one bit per provider plus the
filter). Providers implement the contract in registry.js: coverage,
sequences, nearest-image lookup and a viewer adapter emitting a common
pose. Mapillary is the only registered provider; Google Street View,
KartaView and Panoramax slot in beside it.

Panel: a PROVIDERS chip row (one chip per registered provider, keyless
chips read as errors), relative-day SINCE options, a provider-neutral
caption whose link label follows the provider, and no vendor mark in the
header. The panel inner is a rail scroller like CCTV's.

Tests cover the registry, params codec, filter, pick router, UI-state
composition, the provider definition and coverage-tile decoding; the QA
harness switches the provider off and on and checks the filter.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/streetLevelMarkup.test.mjs

@@ -26,7 +26,12 @@ test('Street Level is an ordinary collapsible GEV panel that starts collapsed',
     /<button class="panel-collapse-btn" data-collapse-target="street-level-panel"/,
   );
   assert.match(html, /<span class="panel-title">STREET LEVEL<\/span>/);
-  assert.match(html, /<svg class="sl-mark"/);
+  // Provider-neutral header: no vendor mark; the inner restores its scroll.
+  assert.doesNotMatch(html, /sl-mark|mly-mark/);
+  assert.match(
+    html,
+    /<div class="street-level-panel-inner" data-rail-scroller>/,
+  );
   assert.doesNotMatch(
     html,
     /mapillary-dock|sl-minimized|sl-3d-btn|sl-photoreal-btn/,
@@ -73,6 +78,9 @@ test('the keyless state gates the controls rather than leaving dead buttons', ()
     /sl-keyless|sl-query|sl-results|data-sl-suggestion/,
   );
   assert.match(html, /<fieldset id="sl-controls"/);
+  assert.match(html, /<div id="sl-provider-chips" class="sl-chips"><\/div>/);
+  assert.match(html, /<select id="sl-since"[\s\S]*?value="3652"/);
+  assert.doesNotMatch(html, /value="year:/);
   assert.match(html, /<ul id="sl-legend"/);
   assert.match(html, /id="sl-error"[^>]*role="alert"/);
   assert.match(html, /id="sl-status"[^>]*role="status"/);
@@ -85,7 +93,11 @@ test('the expanded viewer is a modal dialog that restores focus', () => {
 });
 
 test('labels say what the buttons do', () => {
-  for (const label of ['OPEN NEAREST PHOTO', 'CAMERA FOLLOWS VIEW'])
+  for (const label of [
+    'OPEN NEAREST PHOTO',
+    'CAMERA FOLLOWS VIEW',
+    'PROVIDERS',
+  ])
     assert.ok(html.includes(label), label);
   assert.doesNotMatch(
     html,