[P4suta]

Summary

Remove the unused multi-platform image publisher and repeated analysis from maintenance CI.
Keep the complete Linux quality and coverage suite, Windows and macOS tests, and compilation for Java 8, 11, 17, and 21.

Use mise for the same Corretto 21 selection in local commands and CI.
Pin the tested development tools, update Checkstyle to 14.3.0, and align the local Gradle image with the existing 9.8.1 wrapper.
Pin the retained container bases by verified registry digests.
Run the full push check for new branches with an explicit tracked-file list.

Shorten the README and keep detailed commands in the development guide.
Keep the Apache-2.0 license and the existing solution behavior.

Closes #40.

Checklist

• Native macOS mise x -- just build passes with Gradle 9.8.1 and Corretto 21.
• Final-head mise x -- just lint and the normal full pre-push check pass on macOS.
• Compilation passes for Java targets 8, 11, 17, and 21.
• Windows staged checks pass for the changed configuration and documentation.
• Output contracts and the 80% line and 70% branch coverage floors remain unchanged.
• README and detailed development guidance reflect the retained commands.

The current-head hosted matrix and CodeQL remain merge requirements.
Container validation covers configuration and registry digests.
No container build or publication ran.
The existing Gradle 10 deprecation warning remains outside this change.