Move plugin version into .env, fix version-bump workflow to only touch it

The old workflow grepped CMakeLists.txt for the first "VERSION X.Y" match,
which was cmake_minimum_required's own version rather than the project's,
mangling it to 3.27.0.0 on the first real bump. PLUGIN_VERSION in .env is
now the single source of truth for both CMakeLists.txt and flake.nix, and
the workflow's bump/commit steps only ever touch that one file.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

flake.nix

@@ -18,13 +18,23 @@
     let
       system = "x86_64-linux";
       pkgs = import nixpkgs { inherit system; };
+
+      # Read from .env (also read by CMakeLists.txt) rather than a separate
+      # hardcoded string, so .gitea/workflows/version-bump.yml only ever has
+      # to touch that one file for both build systems to stay in sync.
+      pluginVersion =
+        let
+          envLines = pkgs.lib.splitString "\n" (builtins.readFile ./.env);
+          versionLine = pkgs.lib.findFirst (pkgs.lib.hasPrefix "PLUGIN_VERSION=") null envLines;
+        in
+        pkgs.lib.removePrefix "PLUGIN_VERSION=" versionLine;
     in
     {
       # Build with Hyprland's own stdenv (not nixpkgs' default one) so the
       # compiler/libstdc++ ABI matches what Hyprland itself was built with.
       packages.${system}.default = pkgs.hyprland.stdenv.mkDerivation {
         pname = "hypr-chrome";
-        version = "0.1";
+        version = pluginVersion;
         src = self;
 
         nativeBuildInputs = [ pkgs.cmake pkgs.pkg-config ];