feat(error): add error handling foundation (Day 0)

- extractErrorMessage(err: unknown) normalizes any error shape to string
- handleError/handleInfraError dual utilities (user-facing vs infra-only)
- error-classifier extended with ipc/database/filesystem types (9 total)
- Toast rate-limiting (max 3 per type per 30s) in notifications store
- Infrastructure bridges use documented console.warn (recursion prevention)
- 13 new tests for extractErrorMessage

src/lib/adapters/notifications-bridge.ts

@@ -13,7 +13,10 @@ export function sendDesktopNotification(
   body: string,
   urgency: NotificationUrgency = 'normal',
 ): void {
-  invoke('notify_desktop', { title, body, urgency }).catch(() => {
-    // Swallow IPC errors — notifications must never break the app
+  invoke('notify_desktop', { title, body, urgency }).catch((_e: unknown) => {
+    // Intentional: notification daemon may not be running. Cannot use handleInfraError
+    // here — it calls tel.error, and notify() calls sendDesktopNotification, creating a loop.
+    // eslint-disable-next-line no-console
+    console.warn('[notifications-bridge] Desktop notification failed:', _e);
   });
 }