nix: migrate to top-level fetchPnpmDeps and pnpmConfigHook

pnpm_10.fetchDeps / pnpm_10.configHook are deprecated shims on
nixos-unstable and warn on every evaluation. The shims forwarded to
exactly these attributes (fetchDeps passed pnpm = pnpm_10; configHook
propagated pnpm_10, which is already in nativeBuildInputs), so the
pnpmDeps hash is unchanged.

Verified by building against server-deploy's pinned nixpkgs
(56c02bc) via --override-input, and evaluating standalone on the
nixos-26.05 lock.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nx87UjQtd1HS5u4DwCMve8

package.nix

@@ -2,6 +2,8 @@
   lib,
   stdenv,
   pnpm_10,
+  fetchPnpmDeps,
+  pnpmConfigHook,
   nodejs_24,
   makeWrapper,
   # Pin to prisma-engines_6 (6.19.3) — package.json's `@prisma/client` +
@@ -48,8 +50,9 @@ stdenv.mkDerivation (finalAttrs: {
 
   src = ./.;
 
-  pnpmDeps = pnpm_10.fetchDeps {
+  pnpmDeps = fetchPnpmDeps {
     inherit (finalAttrs) pname version src;
+    pnpm = pnpm_10;
     fetcherVersion = 3;
     prePnpmInstall = patchNdk;
     hash = "sha256-gnEfkEmHCRxDcFRlT9rdlUR38xzOdhn8iDKcsYW7QY0=";
@@ -58,7 +61,7 @@ stdenv.mkDerivation (finalAttrs: {
   postPatch = patchNdk;
 
   nativeBuildInputs = [
-    pnpm_10.configHook
+    pnpmConfigHook
     pnpm_10
     nodejs_24
     makeWrapper