feat(infra): add test:tools npm script (B3-1)

Canonical entry point for tools/observer-*.test.mjs Vitest runner.
Closes B3-1 from brain-retro 2026-05-20 (АДДЕНДУМ B3).

Run via: npm run test:tools (in repo root)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -17,7 +17,8 @@
     "check:docs": "run-p lint:md spell links a11y",
     "sast": "semgrep --config=p/php --config=p/javascript --config=p/typescript --config=p/secrets --config=.semgrep.yml --error --time",
     "eval:llm": "promptfoo eval -c docs/ml/promptfoo-example/promptfooconfig.yaml",
-    "brain:dashboard": "node tools/brain-dashboard-server.mjs"
+    "brain:dashboard": "node tools/brain-dashboard-server.mjs",
+    "test:tools": "cd app && npx vitest run --config vitest.config.tools.mjs"
   },
   "devDependencies": {
     "@cspell/dict-en_us": "^4.4.33",