fix(build): rename threadSummary.ts — case-collision broke the Windows release

threadSummary.ts (pure helpers) and ThreadSummary.tsx (chip component) lived in
the same directory differing only by case. On the case-insensitive Windows
release runner, RoomTimeline's extensionless import of ./thread/ThreadSummary
resolved .ts BEFORE .tsx and matched the helper module → rolldown
MISSING_EXPORT "ThreadSummary" — invisible on every Linux/macOS build (and the
cause of the earlier masked pdf.worker failure). Helper module renamed to
threadSummaryData.ts (+ test), 3 importers updated.

Prevention: new caseCollision.test.ts walks src/ and fails on any same-directory
names differing only by case (extensionless compare, so Foo.tsx vs foo.ts is
caught) — verified it fails on the pre-rename tree. Runs in the hard CI gate.

Gates: tsc clean, eslint/prettier clean, build OK, 658/659 tests (1 IDB skip).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/hooks/useThreadSummary.ts

@@ -8,7 +8,7 @@ import {
   RoomEventHandlerMap,
   ThreadEvent,
 } from 'matrix-js-sdk';
-import { getThreadSummary, ThreadSummaryData } from '../features/room/thread/threadSummary';
+import { getThreadSummary, ThreadSummaryData } from '../features/room/thread/threadSummaryData';
 import { threadNotificationsAtom } from '../state/threadNotifications';
 import { getThreadNotificationMode, ThreadNotificationMode } from '../utils/threadNotifications';