chore: upgrade runtime to Bun 1.4.0

- Update Nix flake.nix overlay to use Bun 1.4.0 (overrideAttrs)
- Update CI (setup-bun) to pin bun-version: 1.4.0
- Update package.json packageManager/Dockerfile/vercel.json
- sha256: sha256:Poy0vf7yJ/hzk33QiQj5gnshI5Q7dfbaMD7xgwiyDKw=

.github/workflows/deploy.yml

@@ -29,7 +29,7 @@ jobs:
 
       - uses: oven-sh/setup-bun@v2
         with:
-          bun-version: latest
+          bun-version: "1.4.0"
 
       - name: Install deps (root workspace)
         run: bun install --frozen-lockfile