fix(street-level): review round — safer docking, mount retry, provider fallthrough

- Only a user's own collapse docks a floating window; cockpit entry,
  restores and the Cyber accordion no longer dock it or delete its saved
  place, and the accordion leaves floating windows alone.
- The viewer host records an adapter as active only after its mount
  succeeds, so a library that failed to load once is retried; concurrent
  opens share one mount, and unmounting mid-mount leaves nothing active.
- openNearest tries every active provider; one provider's error (no key,
  offline) no longer hides the others' imagery.
- The SINCE readout shows its cut-off date as soon as the committed value
  matches the thumb, even while the slider keeps focus.
- A floating window that was only dragged is bounded to the viewport and
  scrolls instead of running off-screen.
- getStats summarises coverage (summarizeCoverage) instead of building a
  full UI snapshot every second; disable() uses credits.hideAll(); smaller
  cleanups in the viewer host and sequence snapshot.
- Unit tests: panel docking and header double press, viewer-host mount
  retry/sharing/cancel, coverage summary.

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

src/streetLevelMarkup.test.mjs

@@ -152,7 +152,7 @@ test('the viewer comes first and the panel is a portable, resizable window', ()
   );
   assert.match(
     read('src/ui/panelChrome.js'),
-    /classList\.toggle\('collapsed', nextCollapsed\);\s*this\._panelPosition\?\.onPanelCollapsed\?\.\(panelId, nextCollapsed\)/,
+    /classList\.toggle\('collapsed', nextCollapsed\);[\s\S]{0,200}?if \(explicit && !restore\)\s*this\._panelPosition\?\.onPanelCollapsed\?\.\(panelId, nextCollapsed\)/,
   );
   assert.match(
     controls,