Nix: fix the flake at HEAD (git dependency) and load libdbus/libEGL on NixOS

Cargo.lock now pins storytold/craft-libs by git revision, so the flake failed at
evaluation with "No hash was found while vendoring the git dependency"
(cargoLock.allowBuiltinFetchGit fixes it).

rfd dlopens libdbus-1 for the xdg-desktop-portal file chooser and wgpu may
fall back to libEGL: neither is on NixOS's default library path, so add dbus
and libglvnd to the wrapper's LD_LIBRARY_PATH.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

nix/package.nix

@@ -4,8 +4,8 @@
 #   nix build          # → ./result/bin/lightcraft, ./result/bin/lightcraft-cli
 #
 # Kept in step with the release workflow (.github/workflows/release.yml) and packaging/env.sh:
-#   * `Cargo.lock` drives the dependencies (`cargoLock`), so there is no vendorHash to bump — only
+#   * `Cargo.lock` drives the dependencies (`cargoLock`), so there is no vendorHash to bump. The git
-#     crates.io, no git sources;
+#     source (storytold/craft-libs) is fetched at the revision the lock file pins;
 #   * `CRAFT_FONTS_DIR` embeds the CJK fonts from storytold/craft-fonts (the `craft-fonts`
 #     flake input); without it everything builds and runs, but Japanese and Chinese text have no glyphs;
 #   * the desktop file, hicolor icons and AppStream metadata are the same files the .deb/.rpm ship
@@ -32,6 +32,9 @@
   libxi,
   libxrandr,
   vulkan-loader,
+  libglvnd,
+  # rfd opens libdbus-1 at run time to reach the xdg-desktop-portal file chooser (Open/Save dialogs).
+  dbus,
   # Validates the desktop file and the AppStream metadata we install (as CI does).
   desktop-file-utils,
   appstream,
@@ -56,8 +59,9 @@ let
   appId = "ai.storyteller.lightcraft";
 
   # Libraries the binaries open at run time with dlopen(): nothing links them, so no RPATH points at
-  # them — winit loads libxkbcommon/libxcb, wgpu the Vulkan loader (NixOS patches that loader to
+  # them — winit loads libwayland-client/libxkbcommon/libxcb, rfd libdbus-1, wgpu the Vulkan loader
-  # find the drivers in /run/opengl-driver). The wrapper below points LD_LIBRARY_PATH here.
+  # or libEGL (NixOS patches that loader to find the drivers in /run/opengl-driver). The wrapper
+  # below points LD_LIBRARY_PATH here.
   runtimeLibs = lib.optionals isLinux [
     libxkbcommon
     wayland
@@ -67,6 +71,8 @@ let
     libxi
     libxrandr
     vulkan-loader
+    libglvnd
+    dbus
   ];
 
   # The two native binaries. The wasm app (apps/lightcraft-web) is built by `cargo xtask web`, not
@@ -98,7 +104,11 @@ rustPlatform.buildRustPackage {
       ]);
   };
 
-  cargoLock.lockFile = root + "/Cargo.lock";
+  cargoLock = {
+    lockFile = root + "/Cargo.lock";
+    # The git dependency (storytold/craft-libs) is pinned by revision in Cargo.lock.
+    allowBuiltinFetchGit = true;
+  };
 
   # Both binaries, as the .deb/.rpm install them (`packaging/linux/package.sh`).
   cargoBuildFlags = [