docs: job-DAG queue model; fold agent_power table into broker.sqlite

coordinator.md rewrites the queue section (node inventory, DAG shapes,
resources, desired-state reconciliation, boot reconcile); approvals.md
+ persistence.md + hivectl --graceful help updated to match. agent_power
lives in broker.sqlite like approvals/questions (own connection + busy
timeout) instead of a separate db file.

hive-c0re/src/bin/hivectl.rs

@@ -139,11 +139,11 @@ enum Cmd {
         #[command(flatten)]
         scope: ScopeArgs,
         /// Gracefully quiesce each agent before stopping, instead of a
-        /// hard stop. Each agent is enqueued as a `GracefulStop` on the
-        /// rebuild queue: the harness is signalled, runs one
-        /// stop-checkpoint turn to flush durable `/state`, drains, then
-        /// the container is stopped (bounded by a 3-min timeout that
-        /// falls back to a hard stop). Applies to agents only.
+        /// hard stop. Each agent gets a graceful-stop DAG on the job
+        /// queue: the harness is signalled, runs one stop-checkpoint
+        /// turn to flush durable `/state`, drains, then the container
+        /// is stopped (bounded by a 3-min timeout that falls back to a
+        /// hard stop). All drains overlap. Applies to agents only.
         #[arg(long)]
         graceful: bool,
     },