feat: add ESLint with error-handling rules

Add ESLint v9.35+ with typescript-eslint recommended config and
error-handling rules: preserve-caught-error (enforces { cause } when
re-throwing), no-unused-vars with caughtErrors:all, and
eslint-plugin-no-catch-all (warns on catch blocks that don't rethrow).

Fix existing violations: add error cause to container-runtime rethrow,
prefix unused vars with underscore, remove unused imports.

https://claude.ai/code/session_01JPjzhBp9PR5LtfLWVDrYrH

package.json

@@ -15,6 +15,8 @@
     "prepare": "husky",
     "setup": "tsx setup/index.ts",
     "auth": "tsx src/whatsapp-auth.ts",
+    "lint": "eslint src/",
+    "lint:fix": "eslint src/ --fix",
     "test": "vitest run",
     "test:watch": "vitest"
   },
@@ -27,13 +29,18 @@
     "zod": "^4.3.6"
   },
   "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",
     "husky": "^9.1.7",
     "prettier": "^3.8.1",
     "tsx": "^4.19.0",
     "typescript": "^5.7.0",
+    "typescript-eslint": "^8.35.0",
     "vitest": "^4.0.18"
   },
   "engines": {