docs(tiles): the tile grid in CLAUDE.md, the invariants, the wiki and the Help modal

- CLAUDE.md: a Tile grid paragraph beside the split-pane one (parking, the
  one load queue, the selection and close rules, chords, dividers, auto-join,
  the exited-agent case), tile-grid.js (7.6) in the load order, the
  desktop-gated header markers and the Tiles picker in the z-index stack.
- docs/architecture-invariants.md#tile-grid: the mechanisms and the reason
  behind each rule; the split section now says where a waiting grid load
  differs and that every capture carries a deadline.
- docs/wiki/Tile-Grid.md: the user manual page (turning it on, the ways in, a
  tile's header, keys, leaving, persistence, Split), linked from the sidebar,
  The Dashboard, Keyboard Shortcuts and Settings Reference.
- The Help modal lists the tile chords (pinned in help-modal-shortcuts.test).
- docs/tile-grid-plan.md: status updated, and an "as built" list of where PR 2
  went another way than the spec.

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

src/web/public/index.html

@@ -833,6 +833,15 @@
               <div><kbd>Enter</kbd> / <kbd>Space</kbd></div><div>Activate Focused Tab</div>
             </div>
           </section>
+          <section class="shortcut-section">
+            <h4>Tiles</h4>
+            <div class="shortcuts-grid">
+              <div><kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>G</kbd></div><div>Toggle Tile Grid</div>
+              <div><kbd>Alt/Option</kbd>+<kbd>Shift</kbd>+<kbd>Arrows</kbd></div><div>Focus Tile Left / Right / Up / Down</div>
+              <div><kbd>Alt/Option</kbd>+<kbd>Shift</kbd>+<kbd>Enter</kbd></div><div>Zoom Focused Tile</div>
+              <div><kbd>Ctrl/Cmd</kbd>+<kbd>Click</kbd> a tab</div><div>Add the Session to the Tile Grid</div>
+            </div>
+          </section>
           <section class="shortcut-section">
             <h4>Terminal</h4>
             <div class="shortcuts-grid">