test(auth): add health endpoint unit tests

- Add node:test suite for auth health endpoint covering:
  - 200 with db=reachable when pool.connect succeeds
  - 503 with db=unreachable when pool.connect throws
  - 503 with db=unreachable when query times out
- Add test script to auth/package.json
- Merge dev to resolve 3-commit divergence

Co-Authored-By: Paperclip <noreply@paperclip.ing>

auth/package.json

@@ -7,7 +7,8 @@
     "dev": "tsx watch src/index.ts",
     "build": "tsc",
     "start": "node dist/index.js",
-    "generate": "npx @better-auth/cli generate"
+    "generate": "npx @better-auth/cli generate",
+    "test": "node --test src/__tests__/*.test.ts"
   },
   "dependencies": {
     "bcrypt": "^6.0.0",