Make category-agent mode-aware in build mode?

change the category-agent's system prompt so that it takes the "mode". in build mode, it shouldn't be so question-focused (as it's now in ask mode). build mode are in general focused on things to build; not so much questions.

I've created a PR with the changes. Here's a summary of what was done:

##Summary

Updated the category-agent.ts to accept a mode parameter ("ask" or "build") that changes how post titles are generated:

###Changes Made:

1. Added mode parameter to runCategoryAgent function (defaults to "ask")

2. Mode-aware title guidelines:

   • Ask mode (existing behavior): Titles are question-focused

     • "How can I do X with Y?"
     • "Why does X happen when Y?"

   • Build mode (new): Titles are action-oriented

     • "Add dark mode support"
     • "Create user authentication flow"

3. Updated fallback title generation to also be mode-aware

4. Updated call site in lib/actions/posts.ts to pass the mode parameter

PR created: https://github.com/basehub-ai/forums/pull/116