chore: add ESLint with TypeScript support and baseline config

Install eslint, @eslint/js, and typescript-eslint as dev dependencies.
Add eslint.config.js (flat config) with rules tuned to zero errors on
the current codebase, add ESLint local hook to .pre-commit-config.yaml,
and update the lint:ts npm script to use ESLint directly.

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

package.json

@@ -16,7 +16,7 @@
     "test:py": "pytest tests/ -v",
     "test:coverage": "pytest tests/ --cov=python --cov-report=html --cov-report=term",
     "lint": "npm run lint:ts && npm run lint:py",
-    "lint:ts": "eslint src/ || echo 'ESLint not configured'",
+    "lint:ts": "eslint src/",
     "lint:py": "cd python && black . && mypy . && flake8 .",
     "format": "prettier --write 'src/**/*.ts' && black python/",
     "prepare": "npm run build",
@@ -40,11 +40,14 @@
   },
   "devDependencies": {
     "@cfworker/json-schema": "^4.1.1",
+    "@eslint/js": "^10.0.1",
     "@types/express": "^5.0.5",
     "@types/glob": "^8.1.0",
     "@types/node": "^20.19.0",
+    "eslint": "^10.1.0",
     "nodemon": "^3.0.1",
     "prettier": "^3.8.1",
-    "typescript": "^5.9.3"
+    "typescript": "^5.9.3",
+    "typescript-eslint": "^8.57.2"
   }
 }