docs+comments: say what changed instead of tagging the tracker item

The prose added by this branch named the tracker item in seventeen
places, which check-issue-refs.sh rejects: a `#N` tag is dead weight for
anyone reading the public mirror, where no issue data exists. Each one
now states the fact it was pointing at — the parent field is gone — so
the sentence stands on its own.

Two of those lines also carried a rustdoc break: `[`write`]` in
topology.rs is ambiguous between the module's own `write` fn and the
`write!` macro, which `-D rustdoc::broken-intra-doc-links` fails. Spelled
`[`write()`]`, per rustdoc's own suggestion.

The host_config.rs rewrite is two lines rather than three so the doc
block stays under check-comment-blocks.sh's 30-line ceiling.

hive-c0re/src/workers/auto_update.rs

@@ -267,8 +267,8 @@ pub async fn run(coord: Arc<Coordinator>) -> Result<()> {
 
     let current_rev = current_flake_rev(&coord.hyperhive_flake);
 
-    // Resolve container names to logical agent names, then sort. #4472
-    // removed the parent field this used to depth-sort by; with no
+    // Resolve container names to logical agent names, then sort. The
+    // parent field this used to depth-sort by is gone; with no
     // hierarchy left to respect, alphabetical is the whole order — and it
     // is exactly what the depth sort already produced once every agent
     // was a root.