fix(project): save_project strips comments via yaml.dump — switch to ruamel.yaml

[JesuFemi-O]

Context

#171 switched migrate_project to ruamel.yaml so comments survive a migration round-trip. However save_project still uses plain yaml.dump, so comments written by a user are destroyed on the next tycoon data sources add or any other command that saves the project file.

Goal

Switch save_project to use ruamel.yaml in round-trip mode so comments and blank lines are preserved when the file is modified by tycoon commands.

Notes

Pre-existing issue, not introduced by #171. Flagged during review of #171.

Depends on #171 (ruamel-yaml is already a runtime dep after that merges).