Add Flutter template

flutter.nix

@@ -0,0 +1,47 @@
+{
+  description = "Flutter development for Desktop/Android/Web";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          config = {
+            android_sdk.accept_license = true;
+            allowUnfree = true;
+          };
+        };
+        androidComposition = pkgs.androidenv.composeAndroidPackages {
+          buildToolsVersions = [ "34.0.0" ];
+          platformVersions = [ "29" "30" "31" "33" "34" ];
+          abiVersions = [ "armeabi-v7a" "arm64-v8a" ];
+          extraLicenses = [
+            "android-googletv-license"
+            "android-sdk-arm-dbt-license"
+            "android-sdk-license"
+            "android-sdk-preview-license"
+            "google-gdk-license"
+            "intel-android-extra-license"
+            "intel-android-sysimage-license"
+            "mips-android-sysimage-license"
+          ];
+        };
+      in {
+        devShells.default = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            flutter
+            androidComposition.androidsdk
+            jdk17
+          ];
+
+          ANDROID_SDK_ROOT =
+            "${androidComposition.androidsdk}/libexec/android-sdk";
+          JAVA_HOME = "${pkgs.jdk17}/lib/openjdk";
+        };
+      });
+}