fix: add Android SDK Build-Tools 36.0.0 to Nix flake (#544)

Avoids build failure due to write permission issues on Nix store when Gradle attempts to auto-download Build-Tools 36 for compileSdk 36.

flake.nix

@@ -21,17 +21,17 @@
           };
         };
 
-        buildToolsVersion = "35.0.0";
+        buildToolsVersion = "36.0.0";
         androidSdk = (pkgs.androidenv.composeAndroidPackages {
           # Command-line & platform tools
           cmdLineToolsVersion = "11.0";
           platformToolsVersion = "35.0.2";
 
           # Build tools
-          buildToolsVersions = [buildToolsVersion "34.0.0"];
+          buildToolsVersions = [buildToolsVersion];
 
           # Target platforms (36 required by AGP 9.0.1 / compileSdk 36)
-          platformVersions = ["36" "35" "34"];
+          platformVersions = ["36"];
 
           # Emulator + system images for local AVD testing
           includeEmulator = true;