fix(street-level): settle loading on pan, keep zoom 0, drop late poses

Fixes from gekh's re-review of 061d269, each with a regression test that
fails on the old code:

- A pan that drops a tile still loading now settles the loading count
  (the aborted request no longer owns its key, so its `finally` never
  did), and purges the previous zoom's tiles once nothing is pending.
  LOADING no longer sticks on the status pill and chip.
- Zoom 0 (above 15,000 km) is a zoom: `zoom == null` instead of `!zoom`.
- A pose that arrives after a photo was closed is dropped, in the
  MapillaryJS adapter and in the viewer host, so the marker and sequence
  selection do not come back.
- Ground casting passes the tile's signal to the terrain request, so a
  cancelled tile stops its height batch instead of holding the queue.
- The server's in-memory tile cache honours the 24 h TTL like the disk.
- The viewer's one-time resize runs for every photo, not just the first.

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

src/ui/streetLevelControls.js

@@ -404,6 +404,9 @@ export class StreetLevelControls {
       button.classList.toggle('is-active', active);
       button.setAttribute('aria-checked', String(active));
     }
+    // Track open → closed here too, so the next photo gets its resize.
+    const wasOpen = this._viewerWasOpen;
+    this._viewerWasOpen = state.street.open === true;
     if (!viewer.open) return;
     if (el.imageBy) el.imageBy.textContent = viewer.captionLeft;
     if (el.imageWhen) el.imageWhen.textContent = viewer.captionRight;
@@ -415,8 +418,7 @@ export class StreetLevelControls {
     // Size changes reach the viewer through the ResizeObserver; resizing on
     // every render ran each frame while a panorama was dragged. Opening is the
     // one moment the element may not have reported a size yet.
-    if (state.street.open && !this._viewerWasOpen) this.layer.resizeViewer?.();
-    this._viewerWasOpen = state.street.open === true;
+    if (state.street.open && !wasOpen) this.layer.resizeViewer?.();
   }
 
   _renderMeta(view) {