Live portal: custom layouts are left alone — new streams chime and wait in a draggable tray; Arrange re-grids and returns to auto

layout store (auto/custom + pending), marked custom on manual move (onDidMovePanel outside arrange), sash drag,
stream/group rename. Tray chips: HTML5 drag accepted via onUnhandledDragOver/onDidDrop (position -> direction),
click = new column. WebAudio two-note chime. Gateway page instructions updated. Verified headless (custom vs auto).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

live/src/Tab.jsx

@@ -1,5 +1,6 @@
 import React, { useEffect, useRef, useState } from 'react'
 import { names } from './names.js'
+import { layout } from './layout.js'
 
 // Tab for a stream panel: double-click to rename (viewer-side label, kept in this browser). Empty = back to user · title.
 export default function Tab({ api, params }) {
@@ -11,7 +12,7 @@ export default function Tab({ api, params }) {
   const ref = useRef(null)
   useEffect(() => { if (editing) { ref.current?.focus(); ref.current?.select() } }, [editing])
   const start = e => { e.stopPropagation(); setDraft(custom || ''); setEditing(true) }
-  const commit = () => { if (!editing) return; const v = draft.trim(); names.rename(id, v); api.setTitle(v || base); setEditing(false) }
+  const commit = () => { if (!editing) return; const v = draft.trim(); names.rename(id, v); api.setTitle(v || base); layout.markCustom(); setEditing(false) }
   return (
     <div className="vtab" title={`${base}\ndouble-click to rename`} onDoubleClick={start}>
       {editing