fix: reduce CI noise from apt-get, sdkmanager, stunnel, and Gradle (#140)

- Add -qq to apt-get update/install in Dagger toolchain to suppress
  verbose package-list output (hundreds of lines on cold cache)
- Wrap sdkmanager in silent-on-success pattern — only shows output
  on failure, like the build_runner and flutter pub get steps
- Set debug = warning in stunnel config to suppress LOG5 (info/notice)
  startup lines while keeping LOG4 (warning) and above
- Add org.gradle.welcome=never to android/gradle.properties to
  suppress the "Welcome to Gradle N.NN!" banner
- Filter SKIPPED Gradle tasks, Gradle Daemon startup messages, and
  gcloud support-page promo lines in run_firebase_test.sh

Errors and warnings are preserved in all cases.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/setup_dagger_remote.sh

@@ -34,6 +34,7 @@ cat << EOF > "$STUNNEL_CONF"
 client = yes
 foreground = yes
 pid = /tmp/stunnel.pid
+debug = warning
 ; TCP keepalive on the remote side to prevent NAT/firewall from resetting the connection
 socket = r:SO_KEEPALIVE=1
 socket = r:TCP_KEEPIDLE=10