fix(nix): regenerate bun.nix from bun.lock (#350)

bun.nix (last regenerated in #298) drifted from bun.lock after the dependency updates in #348, leaving the Nix flake build broken: 254 packages missing and 195 stale entries. Regenerated with bun2nix; all 929 entries now match bun.lock exactly.

Also adds a CI step that detects drift after the regenerate step (made blocking in a follow-up commit).

Thanks @Cyberboss.

.github/workflows/nix-build.yml

@@ -55,3 +55,9 @@ jobs:
       - name: Build package
         if: github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v')
         run: nix build --print-build-logs --accept-flake-config
+
+      - name: Check for diffs
+        run: |
+          if ! git diff --quiet; then
+            echo "`bun.nix` is out of date! Run `nix run github:nix-community/bun2nix -- -o bun.nix` on a NixOS system to regenerate it!"
+          fi