Add 💡 Ideas tab?

[scarf005]

currently, general tab is divided into mostly feature request(FR) and megathreads:

• example of feature/balance request: book binder #2292
• example of megathread: AI discussion #2097

maybe searching each would benefit from having separate tabs. for example, dda had general and ideas tab.

[scarf005]

When you delete a category, GitHub will move all discussions in the deleted category to an existing category that you choose.

github discussions support category merging, so let's try out and see if it works.