refactor(runtime): replace Bun dependency with Node fetch

Run Perplexity search and auth requests through pi's Node runtime instead of
shelling out to Bun. Move development and CI commands to npm, add a Node test
build path, and keep OTP auth fail-fast when Set-Cookie headers are not
available.

tsconfig.json

@@ -9,7 +9,7 @@
     "noEmit": true,
     "skipLibCheck": true,
     "esModuleInterop": true,
-    "types": ["bun-types"]
+    "types": ["node"]
   },
   "include": ["src", "test"]
 }