fix: embed_chat_message() function references nonexistent columns

[NOVA-Openclaw]

Problem

embed_chat_message() trigger function references columns that don't exist in the current memory_embeddings table schema:

• Function uses: content_hash, content, metadata, embedding
• Table has: source_type, source_id, content, embedding, confidence, last_confirmed_at

The trigger (trg_embed_chat_message) has been disabled on nova_memory to prevent replication failures. It was previously set to ENABLE REPLICA which masked the bug by only firing during replication (where it would crash the replication worker).

Impact

• No automatic embedding placeholders created for agent_chat messages
• Trigger disabled on nova_memory, dropped entirely on graybeard_memory
• schema.sql contains the stale function definition

Fix

Update embed_chat_message() to match current memory_embeddings schema, or remove the trigger if chat embedding is handled differently now.

Related

• Replace manual schema migrations with migra declarative schema management #128 (declarative schema management would have caught this drift)
• nova-cognition #192 (replication crash caused by this)