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/test/java/com/runicgateway/app/ScaffoldSanityTest.kt

@@ -0,0 +1,25 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package com.runicgateway.app
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Placeholder JVM unit test so the `test` CI gate has something to run in M0.
+ * Real repository / view-model tests arrive with the functional pass (M1+).
+ */
+class ScaffoldSanityTest {
+    @Test
+    fun applicationIdMatchesNamespace() {
+        assertEquals("com.runicgateway.app", BuildConfig.APPLICATION_ID)
+    }
+
+    @Test
+    fun buildConfigIsDebuggableInTest() {
+        // Unit tests run against the debug variant.
+        assertTrue(BuildConfig.DEBUG)
+    }
+}