T2: _launcher.jar — New Module

[Varaniya201]

1. Create new Maven module registration-launcher compiled with --release 11 and --target 11
2. Implement Initialization class with main() as entry point (remove main() from registration-client.jar)
3. Implement ./MANIFEST.MF signature verification using embedded public key
4. Implement ./MANIFEST.MF vs lib/MANIFEST.MF version comparison
5. Implement JRE version detection via System.getProperty("java.version")
6. Implement JRE 11 migration path (step 3): artifact copy/verify, lib.zip download, unzip, exe copy, run.bat backup, launch migration.exe
7. Implement JRE 21 update path (step 5): lib/MANIFEST.MF download & verify, lib.zip resumable download, unzip to .TEMP/
8. Implement step 6 cleanup logic (post-migration artefact removal)
9. Implement JOptionPane-based operator dialogs for all error, info, and prompt states
10. Implement GraphicsEnvironment.isHeadless() guard for headless environments
11. Enforce: no imports from registration-client.jar or any Java 21 JAR in migration code paths
12. Add unit tests for all branching logic (JRE version detection, version comparison, file state checks)