Add a standalone Android app with the same daily reading and config page

android/ links engine/src/ and interpreter/src/ via JNI/CMake (real
astronomy.c, not the watch's size-constrained substitute), rendering
through Jetpack Compose with a burger-menu config page mirroring
WatchConfig and a WorkManager-driven daily notification. Independent
of the watch app - neither requires the other.

build-image now bundles the Android SDK/NDK alongside the Pebble SDK
(VERSION bumped to 2), and .gitea/workflows/build.yml/Makefile/
run-image.sh build and publish the APK the same way as the CLI
tarball and .pbw.

.gitea/workflows/build.yml

@@ -1,11 +1,14 @@
 name: build
 
-# Build a versioned Linux CLI release tarball (see `make package`) and the
-# Pebble watchapp (see `make watchapp`) on every push/PR, plus on-demand
-# via the Gitea "Run workflow" button. Runs inside build-image (see
-# ../../build-image/Dockerfile, built/pushed via ../../build-image.sh and
-# ../../upload-image.sh), which bundles the Pebble SDK alongside the C
-# toolchain.
+# Build a versioned Linux CLI release tarball (see `make package`), the
+# Pebble watchapp (see `make watchapp`), and the Android app (see `make
+# android`) on every push/PR, plus on-demand via the Gitea "Run workflow"
+# button. Runs inside build-image (see ../../build-image/Dockerfile,
+# built/pushed via ../../build-image.sh and ../../upload-image.sh), which
+# bundles the Pebble SDK and the Android SDK/NDK alongside the C
+# toolchain. Unlike the CLI/Pebble build path, the Android build still
+# needs network access at job runtime (Gradle/AGP/androidx dependency
+# resolution) - see the root CLAUDE.md's Android section.
 on:
   push:
   pull_request:
@@ -41,6 +44,9 @@ jobs:
           command -v cc >/dev/null 2>&1 || { echo "PREFLIGHT FAIL: no C compiler (cc) in PATH" >&2; exit 1; }
           command -v make >/dev/null 2>&1 || { echo "PREFLIGHT FAIL: make not in PATH" >&2; exit 1; }
           command -v pebble >/dev/null 2>&1 || { echo "PREFLIGHT FAIL: pebble not in PATH" >&2; exit 1; }
+          command -v java >/dev/null 2>&1 || { echo "PREFLIGHT FAIL: java not in PATH" >&2; exit 1; }
+          [ -n "${ANDROID_HOME:-}" ] || { echo "PREFLIGHT FAIL: ANDROID_HOME not set" >&2; exit 1; }
+          [ -n "${ANDROID_NDK_HOME:-}" ] || { echo "PREFLIGHT FAIL: ANDROID_NDK_HOME not set" >&2; exit 1; }
 
       - name: Build and test
         run: |
@@ -48,6 +54,7 @@ jobs:
           make test
           make package
           make watchapp
+          make android
 
       - name: Upload build artifact
         # v4 uses the newer @actions/artifact backend, which this Gitea
@@ -63,8 +70,14 @@ jobs:
           name: deck-in-a-dash-watchapp
           path: dist/deck-in-a-dash-*.pbw
 
+      - name: Upload android artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: deck-in-a-dash-android
+          path: dist/deck-in-a-dash-*.apk
+
       - name: Publish to dl.ladkau.de
-        # Uploads the tarball and .pbw over SFTP instead of using
+        # Uploads the tarball, .pbw, and .apk over SFTP instead of using
         # actions/upload-artifact (whose zip wrapping can't be disabled).
         # Only runs on push so PR builds don't publish.
         if: gitea.event_name == 'push'
@@ -72,6 +85,7 @@ jobs:
           set -euo pipefail
           TARBALL="$(ls dist/deck-in-a-dash-*-linux-*.tar.gz)"
           PBW="$(ls dist/deck-in-a-dash-*.pbw)"
+          APK="$(ls dist/deck-in-a-dash-*.apk)"
           mkdir -p ~/.ssh
           echo "${{ secrets.DL_SFTP_KEY }}" > ~/.ssh/dl_sftp_key
           chmod 600 ~/.ssh/dl_sftp_key
@@ -81,4 +95,5 @@ jobs:
           -mkdir files/deck-in-a-dash
           put $TARBALL files/deck-in-a-dash/$(basename "$TARBALL")
           put $PBW files/deck-in-a-dash/$(basename "$PBW")
+          put $APK files/deck-in-a-dash/$(basename "$APK")
           EOF