Show blocklist import error badge in navigation

When the most recent scheduled import completed with errors, surface the
failure in the persistent app shell:
- A warning MessageBar appears at top of main content area
- An amber badge is rendered on the Blocklists sidebar nav item

Backend: add last_run_errors: bool | None to ScheduleInfo model and
populate it in get_schedule_info() from the latest import_log row.

Frontend: extend ScheduleInfo type, add useBlocklistStatus polling hook,
wire both indicators into MainLayout.

Tests: 3 new service tests + 1 new router test (433 total, all pass).

backend/tests/test_services/test_blocklist_service.py

@@ -254,7 +254,42 @@ class TestSchedule:
         assert loaded.interval_hours == 6
 
     async def test_get_schedule_info_no_log(self, db: aiosqlite.Connection) -> None:
-        """get_schedule_info returns None for last_run_at when no log exists."""
+        """get_schedule_info returns None for last_run_at and last_run_errors when no log exists."""
         info = await blocklist_service.get_schedule_info(db, None)
         assert info.last_run_at is None
         assert info.next_run_at is None
+        assert info.last_run_errors is None
+
+    async def test_get_schedule_info_no_errors_when_clean(
+        self, db: aiosqlite.Connection
+    ) -> None:
+        """get_schedule_info returns last_run_errors=False when the last run had no errors."""
+        from app.repositories import import_log_repo
+
+        await import_log_repo.add_log(
+            db,
+            source_id=None,
+            source_url="https://example.test/ips.txt",
+            ips_imported=10,
+            ips_skipped=0,
+            errors=None,
+        )
+        info = await blocklist_service.get_schedule_info(db, None)
+        assert info.last_run_errors is False
+
+    async def test_get_schedule_info_errors_flag_when_failed(
+        self, db: aiosqlite.Connection
+    ) -> None:
+        """get_schedule_info returns last_run_errors=True when the last run had errors."""
+        from app.repositories import import_log_repo
+
+        await import_log_repo.add_log(
+            db,
+            source_id=None,
+            source_url="https://example.test/ips.txt",
+            ips_imported=0,
+            ips_skipped=0,
+            errors="Connection timeout",
+        )
+        info = await blocklist_service.get_schedule_info(db, None)
+        assert info.last_run_errors is True