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-auto-join.test.ts

@@ -12,25 +12,13 @@
  * A tile that joined before its pane existed resends its size once the pid
  * appears (the server spawned the pane at its own default size).
  *
- * A tile's + also offers "New session in this case": the normal Run for the
- * case the tile's session belongs to, the toolbar's case put back afterwards.
- *
  * Real code via the shared vm harness (test/mocks/tile-grid-vm.ts); the Run
  * hook in session-ui.js is pinned at the source. Port: N/A.
  */
 import { readFileSync } from 'node:fs';
 import { resolve } from 'node:path';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
-import {
-  FakeEl,
-  FakeTile,
-  body,
-  bySelector,
-  makeGridApp,
-  resetGridHarness,
-  section,
-  type GridApp,
-} from './mocks/tile-grid-vm.js';
+import { FakeEl, FakeTile, makeGridApp, resetGridHarness, section, type GridApp } from './mocks/tile-grid-vm.js';
 
 const IDS = ['s-a', 's-b'];
 const addSession = (app: GridApp, id: string, workingDir = '/w') =>
@@ -137,42 +125,3 @@ describe('a pane that starts after its tile connected (#464)', () => {
     for (const id of IDS) expect(tileOf(id).paneStarted).not.toHaveBeenCalled();
   });
 });
-
-describe('+ / New session in this case', () => {
-  function openMenu(app: GridApp, fromId: string) {
-    app.openTileAddMenu({ stopPropagation: vi.fn(), preventDefault: vi.fn(), currentTarget: null }, fromId);
-    const menu = body.children.find((c) => c.className.includes('tile-add-menu'))!;
-    return menu.children.find((c) => c.className === 'tile-add-new')!;
-  }
-
-  it('runs the normal Run in the tile session case, then puts the toolbar case back', async () => {
-    const app = makeGridApp(IDS);
-    app.cases = [{ name: 'proj', path: '/w' }];
-    app._mobileOverviewCaseFor = (dir: string, cases: Array<{ name: string; path: string }>) =>
-      cases.find((c) => dir.startsWith(c.path)) ?? null;
-    const select = new FakeEl();
-    select.value = 'other-case';
-    bySelector.set('#quickStartCase', select);
-    const calls: string[] = [];
-    app.selectQuickStartCase = vi.fn((name: string) => {
-      calls.push(`case:${name}`);
-      select.value = name;
-    });
-    app.run = vi.fn(async () => calls.push(`run in ${select.value}`));
-    app.openTileGrid(IDS);
-    const item = openMenu(app, 's-a');
-    expect(item.disabled).toBe(false);
-    item.dispatch('click');
-    await vi.waitFor(() => expect(calls).toHaveLength(3));
-    expect(calls).toEqual(['case:proj', 'run in proj', 'case:other-case']);
-    expect(app.selectQuickStartCase).toHaveBeenCalledWith('proj', { save: false });
-  });
-
-  it('is disabled for a session that is not in a case', () => {
-    const app = makeGridApp(IDS);
-    app.cases = [];
-    app._mobileOverviewCaseFor = () => null;
-    app.openTileGrid(IDS);
-    expect(openMenu(app, 's-a').disabled).toBe(true);
-  });
-});