fix: resolve mem-cli build errors

Fix u32 vs i32 type mismatch in agent_handler for PostgreSQL binding
Remove unused imports and variables

crates/mem-cli/src/handlers/agent_handler.rs

@@ -121,7 +121,7 @@ pub async fn register_agent_handler(
     .bind(&body.agent_id)
     .bind(&body.capabilities)
     .bind(&body.webhook_url)
-    .bind(body.rate_limit.unwrap_or(1000))
+    .bind(body.rate_limit.unwrap_or(1000) as i32)
     .execute(&state.pool)
     .await;