Clarify manual and AI title actions in the thread menu

[maurorozco]

The thread context menu currently offers Rename thread and Regenerate title. Both change the same title, but the labels switch between “thread” and “title” and leave the manual-versus-AI distinction implicit.

Could these be labeled consistently and make that distinction explicit?

• Rename thread → Edit title… — manually enter a title.
• Regenerate title → Generate title with AI — automatically generate a replacement.

Both actions are useful; this is a small wording improvement, with no behavior change proposed. Encountered in T3 Code v0.0.39 on macOS.