feat(#2485): remove vestigial Noop + StartupSweep residuals

Since the boot sweep (#2450) and meta-update cascade (#2476) became
single DAGs that grow subgraphs in-place, nothing constructs the old
fan-out anchors/parents anymore:

- NodeKind::Noop (the old boot_root grouping anchor) — no constructors.
- Template::StartupSweep / Source::StartupSweep (the old fan-out parent
  template + cascade-child source) — replaced by Template::Boot and
  Source::AutoUpdate/MetaUpdate respectively.

Drops the three variants + their as_str arms + the Noop executor arm, and
refreshes the stale fan-out/anchor doc comments (Boot/MetaUpdate/Source
docs, coordinator.md, dashboard.md). Frontend: the queue-kind glyph moves
from the dead startup_sweep to boot (which had none), and the dead
rqe-source-startup_sweep style is dropped.

No behaviour change — pure dead-variant removal.

hive-c0re/src/job_queue/model.rs

@@ -115,11 +115,6 @@ pub enum NodeKind {
     /// deploy stays inside `actions.rs` in v1 — deliberately not
     /// modeled as scheduler nodes (see the design doc §9).
     ApprovalDeploy,
-    /// No-op anchor that completes immediately with no work. Vestigial since
-    /// the boot sweep became one in-DAG graph (no `boot_root` anchor / child
-    /// DAGs) — slated for removal with the other `StartupSweep` residuals.
-    /// Holds no lease and no build slot.
-    Noop,
     /// Write the agent's durable power intent (`wanted = Up` when `up`, else
     /// `Offline`) as a first-class DAG node, at the head of a power-op
     /// template so the downstream `Reconcile` reads it. Replaces the old
@@ -154,7 +149,6 @@ impl NodeKind {
             NodeKind::WriteDropin => "write_dropin",
             NodeKind::WritePermFile => "write_perm_file",
             NodeKind::ApprovalDeploy => "approval_deploy",
-            NodeKind::Noop => "noop",
             NodeKind::SetWanted { .. } => "set_wanted",
         }
     }