ci: Add lib-vt Android support (#10925)

The PR introduces `lib-vt` Android support as discussed in #10902. 

A few more notes:

- Introduces new CI for Android builds as a change requires NDK to be
configured.
- To build locally, it is required to have the NDK installed in the
system and either have the path exported via `ANDROID_NDK_HOME` pointing
to the exact NDK path or `ANDROID_HOME` or `ANDROID_SDK_ROOT` pointing
at the Android SDK path from which the build system will infer the NDK
path and version.
- 16kb page size alignment is configured for Android 15+. Builds are
backward compatible with 4kb page size devices.

.github/workflows/test.yml

@@ -88,6 +88,7 @@ jobs:
       - build-examples
       - build-flatpak
       - build-libghostty-vt
+      - build-libghostty-vt-android
       - build-libghostty-vt-macos
       - build-linux
       - build-linux-libghostty
@@ -350,6 +351,57 @@ jobs:
           nix develop -c zig build lib-vt \
             -Dtarget=${{ matrix.target }}
 
+  # lib-vt requires the Android NDK for Android builds
+  build-libghostty-vt-android:
+    strategy:
+      matrix:
+        target:
+          [aarch64-linux-android, x86_64-linux-android, arm-linux-androideabi]
+    runs-on: namespace-profile-ghostty-sm
+    needs: test
+    env:
+      ZIG_LOCAL_CACHE_DIR: /zig/local-cache
+      ZIG_GLOBAL_CACHE_DIR: /zig/global-cache
+      ANDROID_NDK_VERSION: r29
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Setup Cache
+        uses: namespacelabs/nscloud-cache-action@4d61c33d0b4333a518e975a0c4de7633d28713bb # v1.4.1
+        with:
+          path: |
+            /nix
+            /zig
+            ~/Android/ndk
+
+      # Install Nix and use that to run our tests so our environment matches exactly.
+      - uses: cachix/install-nix-action@2126ae7fc54c9df00dd18f7f18754393182c73cd # v31.9.1
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: cachix/cachix-action@3ba601ff5bbb07c7220846facfa2cd81eeee15a1 # v16
+        with:
+          name: ghostty
+          authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+
+      - name: Setup Android NDK
+        run: |
+          NDK_ROOT="$HOME/Android/ndk"
+          NDK_DIR="$NDK_ROOT/android-ndk-${{ env.ANDROID_NDK_VERSION }}"
+          if [ ! -d "$NDK_DIR" ]; then
+            curl -fsSL -o /tmp/ndk.zip \
+              "https://dl.google.com/android/repository/android-ndk-${{ env.ANDROID_NDK_VERSION }}-linux.zip"
+            mkdir -p $NDK_ROOT
+            unzip -q /tmp/ndk.zip -d $NDK_ROOT
+            rm /tmp/ndk.zip
+          fi
+          echo "ANDROID_NDK_HOME=$NDK_DIR" >> "$GITHUB_ENV"
+
+      - name: Build
+        run: |
+          nix develop -c zig build lib-vt \
+            -Dtarget=${{ matrix.target }}
+
   build-linux:
     strategy:
       fail-fast: false