chore(scaffold): M0 — Gradle + Compose + Hilt skeleton with CI

Stand up the Android-app repo per docs/android/PLAN.md M0: a buildable
Kotlin + Jetpack Compose (Material 3) single-activity skeleton wired for
Hilt, ready for the M1-M4 functional pass.

- Gradle 8.7 wrapper (chmod +x, and re-chmod'd in CI); AGP 8.6.1 /
  Kotlin 2.0.20, JDK 17, minSdk 29, target 35, applicationId com.runicgateway.app.
- Version catalog (gradle/libs.versions.toml) pins the full planned stack
  (Compose, Hilt, Retrofit/OkHttp + kotlinx.serialization, DataStore,
  security-crypto, Coil, Navigation) so later milestones reference by alias.
- RunicGatewayApp (@HiltAndroidApp) + MainActivity (Compose) + ui/theme/*;
  externalized strings; adaptive launcher icon; backup rules exclude the
  token store / DataStore (no session material off-device).
- CI: .gitea/workflows/pr-checks.yml gates PRs with lint + test + assembleDebug.
  Installs JDK 17 via apt (the runner can't resolve api.adoptium.net, so
  actions/setup-java is avoided) and the SDK via sdkmanager; chmods gradlew
  in-step because this runner's checkout drops the git executable bit.

Verified locally against the Android Studio SDK (platform 35 + build-tools
35.0.0): `./gradlew lint test assembleDebug` passes and produces a debug APK.

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

app/src/main/res/values/themes.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- SPDX-License-Identifier: GPL-3.0-or-later -->
+<!--
+  Base XML theme used by the manifest before Compose takes over. The live UI
+  theme is defined in Kotlin (ui/theme/Theme.kt); this only sets the window
+  background / status-bar behavior for launch.
+-->
+<resources>
+    <style name="Theme.RunicGateway" parent="android:Theme.Material.Light.NoActionBar" />
+</resources>