feat(street-level): Street View polish — name, filters, legend, marker

- The chip reads GOOGLE STREET VIEW (and its caption link likewise).
- Providers declare the imagery filters they honour (`filters`, default
  pano + since). Street View declares none: every panorama is 360° and it
  draws no coverage to thin, so its lookups ignore the filters and the
  panel hides IMAGERY and SINCE while it is the only lit provider.
- The legend lists only providers that draw coverage lines, with
  Selected only beside one: Street View alone shows no legend.
- Providers may pick their on-globe marker (`marker`); Street View's is a
  Google-blue field-of-view cone from a white-ringed dot, in place of
  GEV's amber pin, and switches back for a Mapillary photo.

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

src/ui/templates/layer-panels.html

@@ -118,7 +118,7 @@
             <!-- A missing key gates the filters only: the chips above stay
                  focusable so their tooltip can say how to add the key. -->
             <fieldset id="sl-controls" class="sl-controls">
-              <div class="sl-filters" role="group" aria-label="Imagery filters">
+              <div id="sl-pano-row" class="sl-filters" role="group" aria-label="Imagery filters">
                 <span class="cctv-summary-label">IMAGERY</span>
                 <div class="sl-seg" role="radiogroup" aria-label="Panorama filter">
                   <button type="button" class="sl-seg-btn is-active" data-sl-pano="all" role="radio" aria-checked="true">ALL</button>
@@ -126,7 +126,7 @@
                   <button type="button" class="sl-seg-btn" data-sl-pano="flat" role="radio" aria-checked="false" tabindex="-1">FLAT</button>
                 </div>
               </div>
-              <div class="sl-since">
+              <div id="sl-since-row" class="sl-since">
                 <label class="cctv-summary-label" for="sl-since">SINCE</label>
                 <input id="sl-since" class="sl-range" type="range" min="0" max="8" step="1" value="0" aria-valuetext="ANY DATE" aria-describedby="sl-since-label" />
                 <output id="sl-since-label" class="sl-since-label" for="sl-since">ANY DATE</output>