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/ui/panelChrome.js

@@ -430,6 +430,8 @@ export class PanelChrome {
         if (
           peer !== panelEl &&
           peer.matches('[data-panel-id]') &&
+          // A floating window is not part of the rail's accordion.
+          !peer.classList.contains('panel-floating') &&
           !peer.hidden
         ) {
           this.setPanelCollapsed(peer.id, true, {
@@ -557,7 +559,10 @@ export class PanelChrome {
       }
     }
     panelEl.classList.toggle('collapsed', nextCollapsed);
-    this._panelPosition?.onPanelCollapsed?.(panelId, nextCollapsed);
+    // Only a user's own collapse docks a floating window; cockpit entry,
+    // restores and accordion peers must not discard where they put it.
+    if (explicit && !restore)
+      this._panelPosition?.onPanelCollapsed?.(panelId, nextCollapsed);
     if (
       nextCollapsed &&
       this.cockpitView?.active &&