refactor(ui): remove floating, resizable rail panels

PR #768 bundled a portable-panel windowing system with the Street Level
layer. Remove it so CCTV and Street Level are ordinary docked right-rail
panels again, as on main before the merge.

Removed:
- header drag to float, 8-way edge/corner resize, double-press snap-back,
  dockOnCollapse, command-dock clearance, float hint toast, floating z floor,
  persisted floating geometry and ResizeObserver re-clamping
  (panelPositionControls.js restored to its pre-#768 version)
- src/ui/panelResize.js and its tests, panelDock.test.mjs
- onPanelResized/dockPanel wiring in PanelChrome, the application shell and
  StreetLevelControls (EXPAND/SHRINK no longer docks)
- :not(.panel-floating) guards and .panel-floating/.panel-portable/resize CSS
- qa:panel-resize, qa-panel-resize.mjs, qa-panelDrag.mjs, their tests, the
  CI "Portable panel gate" step, QA_FAIL_ON_RETRY, and the Street Level
  gate's float/resize/dock steps
- floating-panel docs in README, CHANGELOG, CURRENT-STATE, KNOWN-ISSUES

Kept: the Street Level panel as a docked rail panel (share/cockpit/rail
lists, layout controller, rail and Cyber CSS, EXPAND viewer), and the
independent right-rail alignment fix (settledLeftRailTop, 9dde7b4).

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

src/ui/panelRails.test.mjs

@@ -113,10 +113,7 @@ function element(
     getBoundingClientRect() {
       return this.rect;
     },
-    matches: (selector) =>
-      selector === '[data-panel-id]' ||
-      (selector === '[data-panel-id]:not(.panel-floating)' &&
-        !classes.has('panel-floating')),
+    matches: (selector) => selector === '[data-panel-id]',
     contains(target) {
       return (
         target === this || this.children.some((child) => child.contains(target))
@@ -325,28 +322,6 @@ test('right layout retains Display allocation during measurement and caps restor
   );
 });
 
-test('right rail neither measures nor allocates a panel floating out of it', () => {
-  const f = fixture('right');
-  f.expand(f.first, 900);
-  f.expand(f.second, 300);
-  f.first.classList.add('panel-floating');
-  f.first.style.setProperty('--right-panel-allocated-height', '500px');
-  f.first.writes.length = 0;
-  f.run();
-  assert.equal(f.stack.dataset.expandedCount, '1');
-  assert.deepEqual(
-    f.first.writes,
-    [],
-    'a floating panel keeps whatever inline style it left the rail with',
-  );
-  assert.equal(f.first.getAttribute('aria-hidden'), undefined);
-  assert.equal(f.first.classList.contains('layout-auto-collapsed'), false);
-  assert.ok(
-    f.second.style.getPropertyValue('--right-panel-allocated-height'),
-    'the docked panel still receives its allocation',
-  );
-});
-
 test('right rail aligns to the current left rail and excludes hidden obstacles', () => {
   const f = fixture('right');
   f.options.leftStack.rect.top = 200;