feat(tiles): no + in the tile header (owner decision 9)

Owner: "remove the + button from these views". The tile header is now
● name ... ⋯ ⤢ ×. Gone with it, because nothing else used them: the +
menu (openTileAddMenu, closeTileAddMenu and their hooks in closeTileGrid
and the global Escape handler), its "New session in this case" entry and
runInCaseForTiles, the .tile-add-empty rules, the four i18n entries only
the menu showed, and buildTilePickerSessions' exclude argument (only the
menu passed it).

Every other way of adding tiles stays and needed nothing from the menu:
the Tiles button and its right-click picker, Ctrl/Cmd+click on a tab,
dragging a tab onto a tile or an empty slot, "Open group as tiles", and
Run joining the open grid (_joinTileGridFromRun). The picker list, the
cap helper _tileGridLimit and the user-text skip on names are shared and
kept.

Tests: the + menu cases (picker, cap, auto-join, the zh-CN harvest) are
removed; tile-grid-chrome pins the header as exactly ⋯ ⤢ × with no add
menu or runInCaseForTiles left on the app.

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

test/tile-grid-picker.test.ts

@@ -1,5 +1,5 @@
 /**
- * @fileoverview The header Tiles button, its picker, and a tile's + menu.
+ * @fileoverview The header Tiles button and its picker.
  *
  * - The button is opt-in (`showTileGridButton`, hidden by its `--hidden` marker
  *   class) and hard-gated to desktop widths like Split: a JS width check plus a
@@ -12,8 +12,8 @@
  *   opens the grid on the checked ones, focusing the active session if checked.
  * - Escape closes it, and its close method is idempotent (the global Escape
  *   handler calls every close method).
- * - A tile's + lists the open sessions not yet tiled; picking one adds and
- *   focuses it; a grid that holds what the window fits disables them.
+ * - A tile has no + (owner decision 9): tiles are added from this picker,
+ *   Ctrl/Cmd+click, a dragged tab, a tab group or Run.
  *
  * Real code via the shared vm harness (test/mocks/tile-grid-vm.ts). Port: N/A.
  */
@@ -26,7 +26,6 @@ import {
   bySelector,
   makeGridApp,
   resetGridHarness,
-  section,
   windowStub,
   type GridApp,
 } from './mocks/tile-grid-vm.js';
@@ -184,11 +183,10 @@ describe('the picker', () => {
     expect(() => app.closeTilePicker()).not.toThrow();
   });
 
-  it('the global Escape handler closes the picker and the + menu', () => {
+  it('the global Escape handler closes the picker', () => {
     const src = readFileSync(resolve(import.meta.dirname, '../src/web/public/app.js'), 'utf8');
     const escape = src.slice(src.indexOf("if (e.key === 'Escape') {"), src.indexOf('Option/Alt session navigation'));
     expect(escape).toContain('this.closeTilePicker?.();');
-    expect(escape).toContain('this.closeTileAddMenu?.();');
   });
 
   it('refuses in a narrow window', () => {
@@ -198,44 +196,3 @@ describe('the picker', () => {
     expect(picker()).toBeNull();
   });
 });
-
-describe("a tile's + menu", () => {
-  const addMenu = () => body.children.find((c) => c.className.includes('tile-add-menu')) ?? null;
-  const addButtonOf = (id: string) =>
-    (section.children.find((el) => el.dataset.sessionId === id) as FakeEl).children[0].children[2].children.find((b) =>
-      b.className.includes('tile-add')
-    ) as FakeEl;
-
-  it('lists the open sessions not yet tiled; picking one adds and focuses it', () => {
-    const app = makeGridApp(IDS);
-    app.openTileGrid(['s-a', 's-b']);
-    app.markIdleAlertSeen.mockClear();
-    addButtonOf('s-a').dispatch('click', { stopPropagation: vi.fn(), currentTarget: null });
-    const items = addMenu()!.children.filter((i) => i.className !== 'tile-add-new');
-    expect(items.map((i) => i.children[0].textContent)).toEqual(['s-other', 's-c']);
-    items[1].dispatch('click');
-    expect(app._tileGrid.ids).toEqual(['s-a', 's-b', 's-c']);
-    expect(app.activeSessionId).toBe('s-c');
-    expect(app.markIdleAlertSeen).toHaveBeenCalledWith('s-c');
-    expect(addMenu()).toBeNull();
-  });
-
-  it('a grid holding what the window fits disables the entries', () => {
-    const app = makeGridApp(IDS);
-    app.openTileGrid(['s-a', 's-b']);
-    const sectionRect = section.getBoundingClientRect;
-    section.getBoundingClientRect = () => ({ width: 1000, height: 400, top: 0, left: 0, right: 1000, bottom: 400 });
-    app.openTileAddMenu({ stopPropagation: vi.fn(), preventDefault: vi.fn(), currentTarget: null });
-    expect(addMenu()!.children.every((i) => i.disabled)).toBe(true);
-    section.getBoundingClientRect = sectionRect;
-  });
-
-  it('closing the grid closes it', () => {
-    const app = makeGridApp(IDS);
-    app.selectSession = vi.fn();
-    app.openTileGrid(['s-a']);
-    app.openTileAddMenu({ stopPropagation: vi.fn(), preventDefault: vi.fn(), currentTarget: null });
-    app.closeTileGrid({ reselect: false });
-    expect(addMenu()).toBeNull();
-  });
-});