feat(android): add screen sender first slice (#104)

Add the Android 14+ MediaProjection direct-child sender, focused protocol tests, compile gate, and durable mobile/TV capability boundaries. Local official-SDK acceptance passed after GitHub runners were blocked before step execution by account billing.

.github/workflows/android-sender.yml

@@ -0,0 +1,34 @@
+name: Android sender compile
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - "android/sender/**"
+      - ".github/workflows/android-sender.yml"
+  push:
+    branches:
+      - main
+    paths:
+      - "android/sender/**"
+      - ".github/workflows/android-sender.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  compile:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v6
+      - name: Set up Java
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: "17"
+      - name: Test protocol core
+        run: ./android/sender/gradlew -p android/sender -PprotocolOnly=true :protocol:test --no-daemon
+      - name: Compile debug APK
+        run: ./android/sender/gradlew -p android/sender :app:assembleDebug --no-daemon