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/templates.rs

@@ -210,11 +210,10 @@ pub fn meta_update(
     }
 }
 
-// The boot is now assembled inline in `workers/auto_update.rs::submit_boot_tree`
-// as ONE DAG (a sweep `MetaLock` root that grows rebuild subgraphs in-DAG, plus
-// a `Reconcile` root per drifted agent) — no `boot_root` Noop anchor, no
-// `startup_sweep` parent template, no per-agent child DAGs. The old single-use
-// `boot_root` / `startup_sweep` builders were inlined there and removed.
+// The boot is assembled inline in `workers/auto_update.rs::submit_boot_tree`
+// as ONE `Boot` DAG (a sweep `MetaLock` root that grows rebuild subgraphs
+// in-DAG, plus a `Reconcile` root per drifted agent) — no anchor node and no
+// per-agent child DAGs.
 
 /// Validate a spec before it enters the queue: node ids are dense
 /// (index = id), deps reference existing nodes, and the dep graph is