Switch Bun builds to copyfile backend

- Use `--backend=copyfile` during `bun install`
- Copy `node_modules` with symlink preservation via `cp -LR`

packages/common.nix

@@ -62,6 +62,7 @@ in {
         bun install \
           --frozen-lockfile \
           --ignore-scripts \
+          --backend=copyfile \
           --linker=hoisted \
           --no-progress \
 ${renderBunFilters filters}
@@ -72,7 +73,7 @@ ${renderBunFilters filters}
       installPhase = ''
         runHook preInstall
 
-        cp -R ./node_modules $out
+        cp -LR ./node_modules $out
 
         runHook postInstall
       '';