fix(ui): floating panels stay on-screen and clear of the command dock

From gekh's review of #768, each with a test that fails before:

- P2: a floating panel whose content grows (CCTV expanded, a photo opened)
  is pulled back on-screen: every portable panel is observed and re-clamped,
  not only on window resize.
- P2: a floating header can never land under #command-dock or the voice
  pill (the rail's stacking context paints below them): clamping keeps the
  header clear of their rects on drag, restore and every re-clamp.
- A live window resize shrinks a floating window wider or taller than the
  viewport; Cyber's accordion no longer collapses docked panels when a
  floating one opens.
- The three pointer gestures share one helper (threshold, mouse/pen only,
  cancel reverts), and the header-drag threshold now has a test.

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

src/ui/panelChrome.js

@@ -419,12 +419,15 @@ export class PanelChrome {
       panelEl.classList.contains('cyber-accordion-collapsed');
     // A user opening a Cyber rail panel owns the whole accordion, including
     // peers that were only presentation-collapsed during a saved-state restore.
+    // A floating window is outside the accordion both ways: opening one
+    // leaves the rail's panels as they are.
     if (
       explicit &&
       !restore &&
       !nextCollapsed &&
       document.documentElement?.dataset.uiTheme === 'cyber' &&
-      panelEl.parentElement === this._rightPanelStack
+      panelEl.parentElement === this._rightPanelStack &&
+      !panelEl.classList.contains('panel-floating')
     ) {
       for (const peer of this._rightPanelStack.children) {
         if (