fix(telemetry): silent-fs-error test exercises the actual code path

Earlier test used '/proc/0/...' as the unwritable dir. On Windows this
resolved to 'C:\proc\0\...' and mkdir({recursive: true}) silently created
it — the silent code path was never exercised, plus filesystem side-effect
leaked outside the test tmpdir.

Replace with a path that points to an existing file (mkdir on a file path
fails on every platform). Also add a companion test that confirms silent
is opt-in: without {silent: true}, the same fs failure DOES throw.

7 tests pass (was 6).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/TelemetryService.test.ts

@@ -58,17 +58,32 @@ describe('TelemetryService.emit', () => {
   });
 
   it('emit is silent (does not throw) when fs write fails — invariant: telemetry never breaks app', async () => {
-    // Pass a non-writable path; emit should swallow the error.
+    // Make the "dir" actually a file so mkdir({recursive:true}) reliably fails on every platform.
+    // (Earlier draft used /proc/0/... which on Windows resolves to C:\proc\0\... and
+    // mkdir({recursive:true}) silently *creates* it, leaking filesystem side-effects + the
+    // silent code path was never exercised.)
+    const blockingFile = join(dir, 'this-is-a-file-not-a-dir');
+    writeFileSync(blockingFile, '');
     const svc = new TelemetryService(
-      '/proc/0/no-such-thing-readonly',
+      blockingFile,
       () => new Date('2026-05-01T12:00:00Z'),
       14,
       { silent: true }
     );
-    // Should resolve, not throw
     await expect(svc.emit({
       kind: 'capture',
       payload: { noteId: 'n1', rawTextLength: 1, hasMedia: false }
     })).resolves.toBeUndefined();
   });
+
+  it('emit DOES throw when fs write fails AND silent is not set (default)', async () => {
+    // Companion case — confirms silent is opt-in. Without silent, fs failure surfaces.
+    const blockingFile = join(dir, 'block-default');
+    writeFileSync(blockingFile, '');
+    const svc = new TelemetryService(blockingFile, () => new Date('2026-05-01T12:00:00Z'));
+    await expect(svc.emit({
+      kind: 'capture',
+      payload: { noteId: 'n1', rawTextLength: 1, hasMedia: false }
+    })).rejects.toThrow();
+  });
 });