#11202 Feat/goal objective comments

Make comments work on objectives, with replies and delete

• The comment box in the objective details popup did nothing; it now saves comments and shows them in a new Comments tab.
• Each comment shows who wrote it and when, in a clean chat-style layout.
• People can reply to a comment; replies are grouped in a small thread under it, like Slack or Discord.
• People can delete their own comments with a trash icon and a quick inline confirmation; admins can delete any comment.
• All new text is translated into the app's supported languages.

https://github.com/user-attachments/assets/44a9b37c-4261-441f-acc9-8192ad447963