build(coverage): finish wiring JaCoCo unit-test coverage reporting

Completes the crash-interrupted #192 WIP (app/build.gradle.kts already had a
jacocoTestReport task and toolVersion pin recovered onto build-192-jacoco):

- Move the JaCoCo tool version into gradle/libs.versions.toml instead of a
  hardcoded string in app/build.gradle.kts, matching how every other plugin
  version in this repo is sourced.
- Fix the generated-code exclusion list against the real compileDebugKotlin
  output (verified by inspecting the compiled class tree): Room's
  KSP-generated `_Impl` DAOs/database and the Compose compiler's per-file
  ComposableSingletons holders are the only generated code that actually
  lands in classDirectories, since Hilt/Dagger's generated Java and AGP's
  BuildConfig/R/Manifest are compiled by a separate javac task this report
  never reads. Drop the blanket `**/*$$*` exclude the WIP had — it was
  silently discarding ~200 real classes' worth of coverage on Kotlin's own
  `$$inlined$` synthetic classes (e.g. Flow.map { ... } transforms in the
  repositories), which is hand-written logic, not generated boilerplate.
- Add Hilt_*/Dagger* prefix patterns so the (currently inert,
  belt-and-suspenders) Hilt exclusions are actually correct if the
  classDirectories scope ever changes.
- Add a minimal CI step to the existing unit-tests job that runs
  jacocoTestReport and uploads the XML+HTML report as a build artifact.
  No coverage threshold gate yet (a jacocoTestCoverageVerification rule is
  a natural follow-up once there's a baseline).
- Document the new :app:jacocoTestReport task in CLAUDE.md.

Verified on JDK 21: fast gate (assembleDebug, testDebugUnitTest,
compileDebugAndroidTestKotlin, lintDebug, ktlintCheck, detekt) plus
jacocoTestReport all pass, from both a warm and a `clean` build. The
report shows real signal (30% instruction / 38% line coverage) with no
generated classes leaking in.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -89,6 +89,21 @@ jobs:
           path: app/build/reports/tests/testDebugUnitTest/
           if-no-files-found: warn
 
+      # JaCoCo XML + HTML coverage for the JVM unit tests (issue #192). Reporting only — no
+      # threshold gate yet, so a coverage regression does not fail CI (a jacocoTestCoverageVerification
+      # gate is a natural follow-up once there's a baseline to enforce).
+      - name: Generate JaCoCo coverage report
+        if: ${{ !cancelled() }}
+        run: ./gradlew :app:jacocoTestReport --stacktrace
+
+      - name: Upload coverage report
+        if: ${{ !cancelled() }}
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: jacoco-coverage-report
+          path: app/build/reports/jacoco/jacocoTestReport/
+          if-no-files-found: warn
+
   static-analysis:
     name: Static analysis
     runs-on: ubuntu-latest