[M] refactor: move encryptConfig to package module

Move encryptConfig.py from root to src/config_man/encrypt_config.py,
update imports to use package path, and add console script entry point.

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

pyproject.toml

@@ -41,6 +41,7 @@ test = [
 
 [project.scripts]
 config-man = "config_man.cli.main:main"
+config-man-encrypt = "config_man.encrypt_config:main"
 
 [project.urls]
 Homepage = "https://github.com/config-man/config-man"