Faster Android builds: ccache, Gradle build cache, 64-bit only, no release lint

Most of a build was compiling the same C++ twice per APK with nothing reused between builds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011Y2iUsKEWDuRGjK5FPmcUP

deploy/gitea-runner/config.yaml

@@ -20,7 +20,8 @@ container:
   # Use Docker's default network instead of creating one per job: a server with many compose
   # projects runs out of address pools ("all predefined address pools have been fully subnetted").
   network: bridge
-  # The volumes the workflow may mount (Gradle and npm caches), and nothing else.
+  # The volumes the workflow may mount (Gradle, npm and ccache caches), and nothing else.
   valid_volumes:
     - musicshare-gradle
     - musicshare-npm
+    - musicshare-ccache