Fix knowledge card creation flow and bugs

Created by: Edouard-Legoupil

This commit provides a comprehensive fix for several issues related to the knowledge card creation and reference identification process.

The changes include:

1. Frontend (KnowledgeCard.jsx):

   • Modified the 'Identify References' button logic to automatically save a new knowledge card before proceeding. This removes a warning message and streamlines the user workflow.

2. Backend (api/knowledge.py):

   • Corrected a KeyError: 'id' by using the proper user_id key when accessing the current user's ID from the authentication dependency.
   • Ensured that the created_by and updated_by audit columns are correctly populated in the knowledge_cards and knowledge_card_references tables for both creation and update operations. This resolves the original NOT NULL constraint violation.

3. Database (database-setup.sql):

   • Relaxed the one_link_only CHECK constraint on the knowledge_cards table from = 1 to <= 1. This allows a knowledge card to be created without an initial link to a donor, outcome, or field context, which is necessary for the new auto-save workflow.

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