Implement persistent conversational AI chat

crates/bds-core/migrations/20260718000000_initial_schema/up.sql

@@ -199,9 +199,7 @@ CREATE TABLE IF NOT EXISTS chat_messages (
     content TEXT,
     tool_call_id TEXT,
     tool_calls TEXT,
-    created_at INTEGER NOT NULL,
-    cache_read_tokens INTEGER,
-    cache_write_tokens INTEGER
+    created_at INTEGER NOT NULL
 );
 
 CREATE TABLE IF NOT EXISTS ai_providers (

crates/bds-core/migrations/20260719141036_add_chat_cache_token_usage/down.sql

@@ -0,0 +1,3 @@
+-- This file should undo anything in `up.sql`
+ALTER TABLE chat_messages DROP COLUMN cache_write_tokens;
+ALTER TABLE chat_messages DROP COLUMN cache_read_tokens;

crates/bds-core/migrations/20260719141036_add_chat_cache_token_usage/up.sql

@@ -0,0 +1,3 @@
+-- Your SQL goes here
+ALTER TABLE chat_messages ADD COLUMN cache_read_tokens INTEGER;
+ALTER TABLE chat_messages ADD COLUMN cache_write_tokens INTEGER;