Forum-1 Add Create new threads to forums

User should be able to:

Open a New thread screen from a category.
Enter a title.
Enter the post body.
Submit the thread.
Save the thread to Supabase.
Automatically associate it with:
user_id
category_id
creation timestamp.
Navigate to the newly created thread after successful creation.

Start by locating the forum category view, the new-thread screen or route, and the Supabase thread persistence entry point. Trace how the current user and category are available before implementing the flow. Done means users can enter a title and body, submit successfully, see the thread saved with its user, category, and creation timestamp, and land on the new thread.

Written by the indexing model from the issue text.