chore: add CI workflow (typecheck + prettier format check), tsconfig, and prettier formatting

package.json

@@ -26,7 +26,9 @@
   ],
   "scripts": {
     "test": "npm run typecheck && tsx tests/test-pure-functions.ts && tsx tests/test-abort.ts && tsx tests/test-stream.ts && node tests/test-pi-local.mjs",
-    "typecheck": "tsc --noEmit --target ES2022 --module NodeNext --moduleResolution NodeNext --allowImportingTsExtensions --skipLibCheck --types node src/core.ts tests/*.ts",
+    "typecheck": "tsc --noEmit",
+    "format:check": "prettier --check '**/*.{ts,mjs,json,md}'",
+    "format": "prettier --write '**/*.{ts,mjs,json,md}'",
     "test:unit": "tsx tests/test-pure-functions.ts",
     "test:abort": "tsx tests/test-abort.ts",
     "test:stream": "tsx tests/test-stream.ts",
@@ -41,6 +43,7 @@
   "devDependencies": {
     "@mariozechner/pi-coding-agent": "0.72.0",
     "@types/node": "25.6.0",
+    "prettier": "^3.5.0",
     "tsx": "4.21.0",
     "typescript": "6.0.3"
   },