feat(#2569): DB-backed per-agent todo store + mcp.sock upsert/clear/list/mark-done ops

hive-c0re/src/main.rs

@@ -43,6 +43,7 @@ pub(crate) use stats::{
 };
 pub(crate) use stores::{
     approvals, audit_log, broker, build_logs, db, operator_questions, power, scheduled_prompts,
+    todos,
 };
 pub(crate) use workers::{
     agent_sockets, auto_update, crash_watch, knowledge, mcp_sockets, reminder_scheduler,