fix(ui): portable panels survive reloads and answer a real double-click

- The rail's startup move of panels into #right-context-rail cleared every
  panel's inline position, so a window restored as floating dropped back to
  its rail place after a reload. Floating panels now keep their geometry.
- A header double-click never snapped a floating panel back in a real
  browser: the drag handler's pointerdown preventDefault() suppresses the
  mouse events a native dblclick is built from. Two presses within 400 ms and
  6 px (no drag between) are now detected in pointerdown itself.
- Portable specs can ask to dock when collapsed (dockOnCollapse), and
  PanelChrome exposes dockPanel(). Street Level opts in as a portable panel
  (min 320 x 280) with dockOnCollapse.
- qa-panel-resize: the panel reader returns right/bottom (s/e handle points
  were NaN), counts only visible rail panels like the rail does, parks the
  window clear of the voice dock before the resize loop, and names the
  element under the pointer when an assertion fails.

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

docs/KNOWN-ISSUES.md

@@ -58,7 +58,7 @@ Related keys (current versions):
   `'1'` closed, absent means the panel's own default. A view opened from a share
   link ignores the stored value entirely.
 - Panel positions: `godsEyeView.v8.panelPos.<panel-id>` — written only for a
-  portable panel (currently CCTV) lifted out of its rail, as
+  portable panel (CCTV, Street Level) lifted out of its rail, as
   `{ left, top, width, height, floating: true }`. Deleting it, or double-clicking
   the panel header, returns that panel to the rail; docked panels store nothing.
 - CCTV calibration: `godsEyeView.cctv.calibration.v2`