refactor(hive-c0re): shared sqlite open helper with busy timeout

one db::open owns the parent-dir + connection + busy_timeout dance for
every host-side store (broker/approvals/questions/schedules/power in
broker.sqlite, build_logs, audit_log); schema + migrations stay per
store. same-file connections now wait out concurrent writers instead
of risking SQLITE_BUSY.

hive-c0re/src/lib.rs

@@ -27,6 +27,7 @@ pub mod coordinator;
 pub mod crash_watch;
 pub mod dashboard;
 pub mod dashboard_events;
+pub mod db;
 pub mod flake_check;
 pub mod forge;
 pub mod gateway_nginx;