Publish NexU 1.25.0 stable release

[p4535992]

Publish the final NexU 1.25.0 line.

Changes:

• retain the complete README content from the 1.24 release, changing only the runtime and application versions required for 1.25;
• remove the obsolete development-line paragraph requested by the maintainer;
• preserve the complete Windows tray, browser enablement, password-flow and Manage keystores documentation;
• align the application, /v1/status, JavaScript client, tests and CI protocol identifier with nexu:1.25;
• align all Maven modules and native packages with 1.25.0-SNAPSHOT / 1.25.0;
• update Build NexU and Package NexU to Java 21 and remove the remaining active 2.0 checks;
• prepare the stable workflow to promote the exact artifacts from v1.25.0-rc.3 after merge.

Validation:

• v1.25.0-rc.3 published successfully from commit 481544941e0caab8d8e6d2c64c9b8b2cee6b496f;
• Build NexU: success;
• Package NexU Linux: success;
• Package NexU Windows: success;
• packaged Linux application and diagnostic-log smoke test: success;
• Windows portable ZIP and EXE generation: success.