docs(ui): describe portable panel position storage

CURRENT-STATE and KNOWN-ISSUES said the panel position key is never
written; a portable panel now stores its floating window there, so both
documents describe the record and how a header double-click clears it.
CHANGELOG notes the CCTV panel's portable mode.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docs/KNOWN-ISSUES.md

@@ -57,9 +57,10 @@ Related keys (current versions):
 - Panel collapsed state: `godsEyeView.v6.panelCollapsed.<panel-id>` — `'0'` open,
   `'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>` — the versioned name for a
-  stored position. The current layout writes none, so deleting one changes
-  nothing.
+- Panel positions: `godsEyeView.v8.panelPos.<panel-id>` — written only for a
+  portable panel (currently CCTV) 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`
 
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