Split runtime node_modules into reusable layers

- Add shared installFlags support to the common Bun node_modules builder
- Factor base and desktop overlay node_modules derivations for reuse
- Reuse the new runtime node_modules outputs in desktop and server builds

packages/common.nix

@@ -17,6 +17,9 @@
 
   renderBunFilters = filters:
     lib.concatMapStringsSep "\n" (filter: "          --filter ${filter} \\") filters;
+
+  renderBunInstallFlags = flags:
+    lib.concatMapStringsSep "\n" (flag: "          ${flag} \\") flags;
 in {
   inherit workspacePreparePatched;
 
@@ -29,6 +32,7 @@ in {
     src,
     outputHash,
     filters,
+    installFlags ? [],
     extraNativeBuildInputs ? [],
     impureEnvVars ? [],
     extraEnv ? "",
@@ -68,6 +72,7 @@ in {
           --backend=copyfile \
           --linker=hoisted \
           --no-progress \
+${renderBunInstallFlags installFlags}
 ${renderBunFilters filters}
 
         bun --bun ${./scripts/canonicalize-node-modules.ts}