chore: remove unused dependencies (yaml, zod, @vitest/coverage-v8)

None of these are imported or referenced by the main codebase.
yaml had zero imports; zod is only used in container/agent-runner
(which has its own package.json); coverage-v8 was never configured.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -25,15 +25,12 @@
     "better-sqlite3": "11.10.0",
     "cron-parser": "5.5.0",
     "pino": "^9.6.0",
-    "pino-pretty": "^13.0.0",
-    "yaml": "^2.8.2",
-    "zod": "^4.3.6"
+    "pino-pretty": "^13.0.0"
   },
   "devDependencies": {
     "@eslint/js": "^9.35.0",
     "@types/better-sqlite3": "^7.6.12",
     "@types/node": "^22.10.0",
-    "@vitest/coverage-v8": "^4.0.18",
     "eslint": "^9.35.0",
     "eslint-plugin-no-catch-all": "^1.1.0",
     "globals": "^15.12.0",