jobq: templates swallow the DagSpec layer

DagSpec described the graph the templates were about to build, one layer
below the templates themselves. Per #2972 the templates should be that
unit, so the spec type is gone and every declarer writes onto the job
builder directly.

- delete DagSpec<F> and its hand-written Debug impl
- submit(source, reason, declare: impl FnOnce(&Job)) replaces the
  pre-built-spec signature; submit_and_emit follows
- all six templates take &Job; the Source is now the caller's to pass,
  which spawn and approval_deploy previously hardcoded while the other
  four did not
- power_dag dissolves into stop_nodes/start_nodes/restart_nodes, which
  borrow their targets instead of owning them

315 tests pass unchanged.

hive-c0re/src/job_queue/model.rs

@@ -426,44 +426,3 @@ impl NodeKind {
         // - `DeployWindow` brackets a deploy without itself stopping anything.
     }
 }
-
-/// Submit-time spec for a whole DAG: the group's metadata plus the declared —
-/// not yet inserted — nodes. Built by `templates.rs`, inserted by
-/// `JobQueue::submit`.
-///
-/// No DAG-level `agent` — every node carries its own (a DAG can span agents),
-/// and the queue derives per-agent leasing from [`NodeKind::agent`].
-/// Type-specific payloads (`PermChange`'s file payload) ride the node that
-/// consumes them ([`NodeKind::WritePermFile`]), not this generic spec.
-///
-/// There is no separate per-node spec type, and no built job either: `declare`
-/// is a *recipe* the queue runs against a builder `hive_jobq` owns, at the
-/// moment it inserts. A shape that has been declared is therefore always
-/// insertable — a dangling edge or a cycle cannot be expressed, so there is
-/// nothing left for a submit-time validation pass to reject.
-///
-/// Generic over the recipe rather than boxing it: a spec goes from the template
-/// that returns it straight to the `submit` that consumes it, so the closure's
-/// concrete type is known the whole way and needs neither an allocation nor a
-/// `Send` bound. Nothing boxes a recipe any more — a running node grows its DAG
-/// by declaring straight onto the builder it was handed, so there is no recipe
-/// to store and replay across a task boundary.
-pub struct DagSpec<F> {
-    pub source: Source,
-    /// Free-form "why".
-    pub reason: String,
-    /// Declares the DAG's nodes — their edges, grouping and resources — onto
-    /// the builder the queue hands it.
-    pub declare: F,
-}
-
-impl<F> std::fmt::Debug for DagSpec<F> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        // The recipe is a closure; there is nothing to show of it, and its
-        // nodes do not exist until the queue runs it.
-        f.debug_struct("DagSpec")
-            .field("source", &self.source)
-            .field("reason", &self.reason)
-            .finish_non_exhaustive()
-    }
-}