feat(tiles): move tiles by hand, and detach a tile into its own window

Gesture control now moves tiles: with the tile grid open, pinch anywhere
on a tile and carry it onto another tile (they swap) or an empty cell (it
moves there); a session tab carried onto the grid joins it there. The
overlay asks tile-grid.js what is under the hand (tileAtPoint,
tileDropTargetAt) and drops through the mouse drag's own paths
(dropSessionOnTile / dropSessionOnSlot, so _reorderTiles stays the one
move path).

Detach Tiles (App Settings > Appearance, per device, OFF by default,
desktop only):
- a tile's header let go outside the browser window opens the session as
  a pop-out (detachSession, which now takes an optional size and screen
  position), the tile's size, near the drop point, after a 120 ms settle;
- dropped on another Codeman window's tiles it moves there: that window
  docks it through the target's own drop and posts 'tile-adopted' on the
  window channel, and only the window it was dragged from lets go of its
  copy (a last tile goes to the welcome screen, never onto that session);
- a pop-out's title drags back onto any grid: the session is taken back,
  the pop-out is asked to close and is released (stops answering
  roll-calls; one a script cannot close says where the session went), and
  its stale 'detached' answers are ignored for 2 s;
- a tile's menu offers "Open in a new window", and a hand that lets a tile
  go outside the grid pops it out too.

With the setting off nothing changes. No server change.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/mocks/tile-grid-vm.ts

@@ -213,6 +213,8 @@ export const bySelector = new Map<string, FakeEl>();
 export const body = new FakeEl();
 /** The context's `fetch`; a test sets what it answers. */
 export const fetchSpy = vi.fn(async (..._args: unknown[]) => ({ ok: true, json: async () => ({}) }));
+/** What `document.elementFromPoint` answers (the gesture overlay's hit test); a test sets it. */
+export const pointHits: { at: ((x: number, y: number) => FakeEl | null) | null } = { at: null };
 /** `document.addEventListener`, so a test can find a listener the app installed. */
 export const documentAddEventListener = vi.fn();
 export const documentRemoveEventListener = vi.fn();
@@ -280,6 +282,7 @@ const context = vm.createContext({
       return focusedEl;
     },
     getElementById: (id: string) => (id === 'tileGrid' ? section : (bySelector.get(`#${id}`) ?? null)),
+    elementFromPoint: (x: number, y: number) => pointHits.at?.(x, y) ?? null,
     body,
     querySelector: (sel: string) =>
       bySelector.get(sel) ?? (sel === '.main' ? main : sel === '.terminal-wrap' ? wrap : null),
@@ -389,4 +392,5 @@ export function resetGridHarness() {
   main.appendChild(section);
   bySelector.clear();
   body.children = [];
+  pointHits.at = null;
 }