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/utils/caseCollision.test.ts

@@ -0,0 +1,43 @@
+import { strict as assert } from 'node:assert';
+import { test } from 'node:test';
+import { readdirSync } from 'node:fs';
+import { join } from 'node:path';
+
+/**
+ * Guard against same-directory filenames that differ only by case (e.g.
+ * `threadSummary.ts` vs `ThreadSummary.tsx`). On case-insensitive filesystems
+ * (the Windows release runner) an extensionless import of one can resolve to
+ * the OTHER file — rolldown tries `.ts` before `.tsx` — producing
+ * MISSING_EXPORT failures that never reproduce on the Linux/macOS machines the
+ * project is developed and web-deployed on. This broke the desktop release
+ * build twice before being diagnosed; this test makes the collision a local,
+ * immediate failure instead.
+ */
+const findCaseCollisions = (dir: string, collisions: string[]): void => {
+  const entries = readdirSync(dir, { withFileTypes: true });
+  const seen = new Map<string, string>();
+  entries.forEach((entry) => {
+    // Compare basenames without extension: `Foo.tsx` collides with `foo.ts`
+    // because module resolution is extensionless.
+    const stem = entry.isDirectory() ? entry.name : entry.name.replace(/\.[^.]+$/, '');
+    const key = stem.toLowerCase();
+    const existing = seen.get(key);
+    if (existing !== undefined && existing !== stem) {
+      collisions.push(`${dir}: "${existing}" vs "${stem}"`);
+    }
+    if (existing === undefined) seen.set(key, stem);
+    if (entry.isDirectory()) {
+      findCaseCollisions(join(dir, entry.name), collisions);
+    }
+  });
+};
+
+test('no same-directory filenames differing only by case under src/', () => {
+  const collisions: string[] = [];
+  findCaseCollisions('src', collisions);
+  assert.deepEqual(
+    collisions,
+    [],
+    `Case-colliding names break Windows builds:\n${collisions.join('\n')}`,
+  );
+});