fix(tiles): a tile's + menu items get their disabled reason in Chinese

Found live in zh-CN: the + menu's session items stayed titled "The grid
holds at most 6 tiles". Each item carried data-i18n-skip on the whole
button to keep the session name as typed, and the translator skips an
element's attributes along with its text. Only the name is skipped now (a
child span, as the picker does), so the title is translated.

The zh-CN coverage test classified a title inside a skipped subtree as
user text, which is how this got past it; such a label is now a failure
of its own ("no UI label sits inside a skipped subtree").

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

test/tile-grid-cap.test.ts

@@ -67,7 +67,7 @@ describe('every way in stops at the cap', () => {
     const app = fullGrid();
     app.openTileAddMenu({ stopPropagation: vi.fn(), preventDefault: vi.fn(), currentTarget: null }, 's-1');
     const menu = body.children.find((c) => c.className.includes('tile-add-menu'))!;
-    const items = menu.children.filter((c) => c.textContent === 's-7' || c.textContent === 's-8');
+    const items = menu.children.filter((c) => ['s-7', 's-8'].includes(c.children[0]?.textContent ?? ''));
     expect(items).toHaveLength(2);
     for (const item of items) {
       expect(item.disabled).toBe(true);