fix: detect musl/glibc at runtime for correct Claude binary download

Previously used cfg!(target_env = "musl") which checks compile-time,
causing musl-compiled sandbox-agent to always download musl binaries
even on glibc systems like Debian/E2B.

Now checks for /lib/ld-musl-*.so.1 at runtime to detect the actual
system libc and download the correct Claude binary variant.

examples/vercel/tsconfig.json

@@ -1,16 +0,0 @@
-{
-  "compilerOptions": {
-    "target": "ES2022",
-    "lib": ["ES2022", "DOM"],
-    "module": "ESNext",
-    "moduleResolution": "Bundler",
-    "allowImportingTsExtensions": true,
-    "noEmit": true,
-    "esModuleInterop": true,
-    "strict": true,
-    "skipLibCheck": true,
-    "resolveJsonModule": true
-  },
-  "include": ["src/**/*"],
-  "exclude": ["node_modules", "**/*.test.ts"]
-}