chore(sonar): wire JaCoCo coverage and clear actionable smells

Fix the SonarQube coverage gate (0% on new code) — a reporting gap, not a
testing gap: the JVM unit suite already exists but the source-only scan
never received a coverage report.

- app/build.gradle.kts: apply jacoco, enable debug unit-test coverage, add a
  jacocoTestReport task (excludes generated/Hilt/Compose-singleton classes)
- sonar-project.properties: consume the JaCoCo XML; exclude pure-@Composable
  UI from coverage (JVM unit tests can't execute composable bodies)
- .gitea/workflows/sonarqube.yml: run JDK 17 + Android SDK +
  `testDebugUnitTest jacocoTestReport` before the scan

Also clear the three actionable code smells: remove an unused import
(AdminContentScreen), remove an unused parameter (AdminSupportScreen.
RespondDialog), and decompose LoginViewModel.submit() (cognitive complexity
20 -> under 15). The remaining 12 smells (snake_case DTO fields that mirror
the JSON wire contract; Compose/nav complexity) are marked Won't Fix in
SonarQube with rationale.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NgyHnrNa8WwG3doxvxjuCr

.gitea/workflows/sonarqube.yml

@@ -18,11 +18,12 @@
 # SonarQube Quality Gate, so a failing gate does not fail this job — check the
 # dashboard when you want to.
 #
-# Scope: this analyses the Kotlin source directly (the Sonar scanner reads
-# sonar-project.properties). It does NOT run a Gradle build, so no Android SDK /
-# JDK install is needed — the Kotlin analyzer is source-based. See the "Optional
-# enrichment" note in sonar-project.properties for wiring in Android Lint /
-# coverage reports later.
+# Scope: the Sonar scanner reads sonar-project.properties and analyses the Kotlin
+# source directly. Before the scan we run the JVM unit tests + JaCoCo so SonarQube
+# receives real coverage (sonar.coverage.jacoco.xmlReportPaths) — otherwise it
+# reports 0% and the coverage gate fails despite the test suite existing. That
+# Gradle step needs JDK 17 + the Android SDK (same toolchain as pr-checks.yml);
+# the runner container is bare, so base tools are apt-installed first.
 
 name: SonarQube
 
@@ -40,6 +41,16 @@ jobs:
   analysis:
     runs-on: ubuntu-latest
     steps:
+      # The bare runner container lacks git/curl/unzip (checkout + sdkmanager need
+      # them) and we install JDK 17 from the Ubuntu archive rather than
+      # actions/setup-java (this runner can't reach api.adoptium.net). Mirrors
+      # pr-checks.yml — see its header note.
+      - name: Install base tools + JDK 17
+        run: |
+          apt-get update
+          apt-get install -y git curl unzip openjdk-17-jdk-headless
+          echo "JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64" >> "$GITHUB_ENV"
+
       - name: Check out (full history for accurate new-code + blame)
         uses: actions/checkout@v4
         with:
@@ -47,6 +58,31 @@ jobs:
           # compute "new code". A shallow clone degrades both.
           fetch-depth: 0
 
+      - name: Set up Android SDK
+        uses: android-actions/setup-android@v3
+
+      - name: Install Android SDK packages
+        run: |
+          set +o pipefail
+          yes | sdkmanager "platform-tools" "platforms;android-35" "build-tools;35.0.0"
+
+      - name: Cache Gradle
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: gradle-${{ runner.os }}-${{ hashFiles('**/*.gradle.kts', 'gradle/libs.versions.toml', 'gradle/wrapper/gradle-wrapper.properties') }}
+          restore-keys: |
+            gradle-${{ runner.os }}-
+
+      # Produce the JaCoCo XML the scan reports as coverage. Scoped to the debug
+      # variant (matches enableUnitTestCoverage) to keep peak memory down.
+      - name: Unit tests + JaCoCo coverage
+        run: |
+          chmod +x ./gradlew
+          ./gradlew --no-daemon testDebugUnitTest jacocoTestReport
+
       - name: Run SonarQube scan
         uses: sonarsource/sonarqube-scan-action@v4
         env: