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; AGP 8.6.1 / Kotlin 2.0.20, JDK 17, minSdk 29, target 35.
- 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/*.
- Strings externalized from day one; 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
  (JDK 17 + Android SDK on the self-hosted runner; debug builds auto-signed,
  no secrets). Placeholder JVM unit test so the test gate runs.
- .gitattributes forces LF on gradlew so the wrapper runs on the Linux runner.

Verified locally: `gradle help`/`projects` configure the :app module and
resolve all six plugins cleanly (full assemble needs the Android SDK, done in CI).

app id: com.runicgateway.app (PLAN.md §13, pending runicgateway.app domain).

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

app/src/main/java/com/runicgateway/app/MainActivity.kt

@@ -0,0 +1,64 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package com.runicgateway.app
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.tooling.preview.Preview
+import com.runicgateway.app.ui.theme.RunicGatewayTheme
+import dagger.hilt.android.AndroidEntryPoint
+
+/**
+ * Single-activity host. Navigation-Compose and the first-run base-URL flow (§3)
+ * land in M1; this M0 skeleton only proves the Compose + Hilt + theme wiring.
+ */
+@AndroidEntryPoint
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        setContent {
+            RunicGatewayTheme {
+                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
+                    Placeholder(modifier = Modifier.padding(innerPadding))
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun Placeholder(modifier: Modifier = Modifier) {
+    Column(
+        modifier = modifier.fillMaxSize(),
+        horizontalAlignment = Alignment.CenterHorizontally,
+        verticalArrangement = Arrangement.Center,
+    ) {
+        Text(
+            text = stringResource(id = R.string.app_scaffold_ready),
+            style = MaterialTheme.typography.titleLarge,
+        )
+    }
+}
+
+@Preview(showBackground = true)
+@Composable
+private fun PlaceholderPreview() {
+    RunicGatewayTheme {
+        Placeholder()
+    }
+}

app/src/main/java/com/runicgateway/app/RunicGatewayApp.kt

@@ -0,0 +1,15 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ * Runic Gateway — native Android client of a shard's website API.
+ */
+package com.runicgateway.app
+
+import android.app.Application
+import dagger.hilt.android.HiltAndroidApp
+
+/**
+ * Application entry point. Annotated for Hilt so the DI graph is available
+ * to activities, view models, and (from M1) repositories / API services.
+ */
+@HiltAndroidApp
+class RunicGatewayApp : Application()

app/src/main/java/com/runicgateway/app/ui/theme/Color.kt

@@ -0,0 +1,16 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package com.runicgateway.app.ui.theme
+
+import androidx.compose.ui.graphics.Color
+
+// Placeholder palette for the M0 skeleton. The M5 design pass replaces this and
+// derives Material 3 colors from each shard's per-install branding (PLAN.md §3, §5).
+val Purple80 = Color(0xFFD0BCFF)
+val PurpleGrey80 = Color(0xFFCCC2DC)
+val Pink80 = Color(0xFFEFB8C8)
+
+val Purple40 = Color(0xFF6650A4)
+val PurpleGrey40 = Color(0xFF625B71)
+val Pink40 = Color(0xFF7D5260)

app/src/main/java/com/runicgateway/app/ui/theme/Theme.kt

@@ -0,0 +1,53 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package com.runicgateway.app.ui.theme
+
+import android.os.Build
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.material3.dynamicDarkColorScheme
+import androidx.compose.material3.dynamicLightColorScheme
+import androidx.compose.material3.lightColorScheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.platform.LocalContext
+
+private val DarkColorScheme = darkColorScheme(
+    primary = Purple80,
+    secondary = PurpleGrey80,
+    tertiary = Pink80,
+)
+
+private val LightColorScheme = lightColorScheme(
+    primary = Purple40,
+    secondary = PurpleGrey40,
+    tertiary = Pink40,
+)
+
+/**
+ * App theme for the M0 skeleton. Dynamic color (Android 12+) is used when
+ * available; otherwise a static placeholder scheme. The M5 design pass wires
+ * the color scheme to per-shard branding (PLAN.md §3, §5).
+ */
+@Composable
+fun RunicGatewayTheme(
+    darkTheme: Boolean = isSystemInDarkTheme(),
+    dynamicColor: Boolean = true,
+    content: @Composable () -> Unit,
+) {
+    val colorScheme = when {
+        dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
+            val context = LocalContext.current
+            if (darkTheme) dynamicDarkColorScheme(context) else dynamicLightColorScheme(context)
+        }
+        darkTheme -> DarkColorScheme
+        else -> LightColorScheme
+    }
+
+    MaterialTheme(
+        colorScheme = colorScheme,
+        typography = Typography,
+        content = content,
+    )
+}

app/src/main/java/com/runicgateway/app/ui/theme/Type.kt

@@ -0,0 +1,21 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package com.runicgateway.app.ui.theme
+
+import androidx.compose.material3.Typography
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.sp
+
+// Default Material 3 type scale for the skeleton; refined in the M5 design pass.
+val Typography = Typography(
+    bodyLarge = TextStyle(
+        fontFamily = FontFamily.Default,
+        fontWeight = FontWeight.Normal,
+        fontSize = 16.sp,
+        lineHeight = 24.sp,
+        letterSpacing = 0.5.sp,
+    ),
+)