build: remove unused :ammolite module

The :ammolite module contained no production Kotlin/Java sources (just
a manifest, build.gradle, and proguard stubs) and no module in the
codebase imports com.vitorpamplona.ammolite.*.

Removes:
- ammolite/ directory (5 files)
- :ammolite project include in settings.gradle
- implementation project(':ammolite') from :amethyst
- androidTestImplementation project(':ammolite') from :benchmark
- :ammolite:testDebugUnitTest from CI workflow and pre-push hook
- -keep class com.vitorpamplona.ammolite.** rules from
  :amethyst, :commons, and :desktopApp proguard files
- Stale references in CONTRIBUTING.md, CLAUDE.md, and the
  gradle-expert skill dependency-graph doc

Small build-graph win: one fewer module to configure, compile, lint,
and spotless-check on every build, and one fewer unit-test target in
both CI and the local pre-push hook.

.github/workflows/build.yml

@@ -218,7 +218,6 @@ jobs:
             :quartz:jvmTest \
             :commons:jvmTest \
             :nestsClient:jvmTest \
-            :ammolite:testDebugUnitTest \
             :amethyst:testFdroidDebugUnitTest \
             :amethyst:testPlayDebugUnitTest \
             :amethyst:assembleBenchmark \