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/telemetry-bridge.ts

@@ -11,8 +11,11 @@ export function telemetryLog(
   message: string,
   context?: Record<string, unknown>,
 ): void {
-  invoke('frontend_log', { level, message, context: context ?? null }).catch(() => {
-    // Swallow IPC errors — telemetry must never break the app
+  invoke('frontend_log', { level, message, context: context ?? null }).catch((_e: unknown) => {
+    // Intentional: telemetry must never break the app or trigger notification loops.
+    // Cannot use handleInfraError here — it calls tel.error which would recurse.
+    // eslint-disable-next-line no-console
+    console.warn('[telemetry-bridge] IPC failed:', _e);
   });
 }