refactor(web): share alert banner and turn actions, fix restyle leaks

Add AlertBanner and turnActions to replace duplicated markup and
wrappers, and share component-test setup.

Fixes: oversized dismiss, help, rules and skip-link text after the type
ramp collapse; report button hover styled as submit; chat draft lost
when the panel folds; resign/claim/kick styles leaking app-wide.

web/tests/room-code.test.js

@@ -74,7 +74,7 @@ describe('normalizeRoomCode', () => {
 
 	it('handles nothing at all', () => {
 		expect(normalizeRoomCode('')).toBe('');
-		expect(normalizeRoomCode(/** @type {any} */ (undefined))).toBe('');
+		expect(normalizeRoomCode(/** @type {string} */ (/** @type {unknown} */ (undefined)))).toBe('');
 	});
 });