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.
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