fix: port search and dimension safety guardrails

- enforce canonical dimensions across app and MCP surfaces
- prioritize title-first node search in UI and query tools
- add regression tests for ranking and dimension validation

tests/unit/setup.ts

@@ -0,0 +1,5 @@
+import { afterEach, vi } from 'vitest';
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});