[ax] Deprecate -n shortcut for --dry-run

[TomasVotruba]

Why

-n is registered as the short form of --dry-run. In almost every other CLI tool (Symfony Console included) -n means --no-interaction. An agent or user carrying that convention over silently triggers a dry-run when they meant something else - a quiet footgun.

What

Deprecate the -n shortcut without breaking it: when -n is used, warn on stderr and point to the explicit flag.

[WARNING] The "-n" shortcut for "--dry-run" is deprecated and will be removed,
          as it means "--no-interaction" in most CLI tools. Use "--dry-run" instead.

• -n still works exactly as before (dry-run) - no behavior change, just a warning.
• The warning goes to stderr (getErrorStyle), so stdout / --output-format=json stay clean.
• --dry-run is unaffected (no warning).

Removal of the shortcut itself is left for the next major version.

Verification

• rector process -n -> warning on stderr, still dry-runs, stdout clean.
• rector process --dry-run -> no warning.

Note

Whole-repo check-cs is currently red on ConfigInitializer.php / SymfonyStyleFactory.php due to a merge-time rewrite; that is fixed in #8455. Once #8455 lands, rebasing this branch turns CI green. This PR touches only ProcessCommand.php.