fix(street-level): viewer lifecycle, hover cost, keyboard focus, panel lift

From the IC8 review of #768 (P2s), each with a test that fails before:

- Switching the layer off and on during the first photo download no longer
  leaves the viewer stuck on "not mounted": an outdated mount only unmounts
  an adapter nobody else holds and subscribes poses only once current, and
  the MapillaryJS adapter never builds a viewer after it was unmounted.
- Hover picks at most every 120 ms (the CCTV convention), not while the
  camera moves or a button is held, and not after the layer went off.
- Esc shrinks the expanded viewer wherever focus is (document capture), so
  the map keeps its selection, and Tab from outside returns into it.
  Closing a photo moves focus to the panel instead of dropping it on body.
- Portable panels lift only after a mouse or pen moves past the drag
  threshold: a click on a docked panel's edge or a touch swipe on its
  header no longer turns it into a floating window, and pointercancel
  saves nothing and puts the panel back.

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

scripts/format-scope.json

@@ -915,6 +915,7 @@
   "src/ui/streetLevelControls.test.mjs",
   "src/ui/panelDock.test.mjs",
   "src/layers/streetLevel/viewerHost.test.mjs",
+  "src/layers/streetLevel/selection.test.mjs",
   "src/layers/streetLevel/index.test.mjs",
   "scripts/qa-overpass-offload.mjs",
   "src/overpassOffload.test.mjs",