fix(deploy): pin pnpm to 9.15.9 and regenerate lockfile in 9.x format

Last build hit ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING — the Nixpacks
image bundles corepack 0.24.1 which can't hydrate pnpm 11's binary on
Node 22 (known corepack/pnpm/Node interop bug). Rather than fight the
toolchain, downgrade to the version Coolify's Nixpacks already ships
natively: pnpm 9.15.9.

  packageManager: pnpm@9.15.9
  pnpm-lock.yaml regenerated under 9.15.9 (no patchedDependencies hash
  drift, no settings/* block, lockfile version 9.0)

Verified locally: 'pnpm build' produces the same Next 16 output as
before, and the node-fetch-native-with-agent patch is still applied in
node_modules (globalThis.fetch present in the patched agent.cjs). Coolify
should now do 'pnpm i --frozen-lockfile' without any version mismatch.

package.json

@@ -2,7 +2,7 @@
   "name": "lab",
   "version": "0.1.0",
   "private": true,
-  "packageManager": "pnpm@11.1.2",
+  "packageManager": "pnpm@9.15.9",
   "scripts": {
     "dev": "next dev",
     "build": "next build",