test(api): add temporary pocketbase harness for api tests

`pnpm test:api` starts an isolated PocketBase with project migrations and
hooks in a temp dir, provides SDK client helpers and cleans up after the run,
on failure and on SIGINT/SIGTERM. The superuser is generated per instance.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EvmtStx737hu8gXe15e55W

package.json

@@ -7,6 +7,7 @@
         "build": "ng build",
         "watch": "ng build --watch --configuration development",
         "test": "ng test",
+        "test:api": "vitest run --config vitest.api.config.ts",
         "lint": "eslint .",
         "lint:fix": "eslint . --fix",
         "serve:ssr:pchelpcrm": "node dist/pchelpcrm/server/server.mjs",