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/agent_config/topology.rs

@@ -6,7 +6,7 @@
 //! **There is no hierarchy here any more.** The file used to be a map of
 //! `name → parent | null` and this module owned the parent/child tree that
 //! fed `<parent>` / `<children>` routing, the reparenting API and the
-//! dashboard's tree view. All of that is gone (#4472); what the file is
+//! dashboard's tree view. All of that is gone; what the file is
 //! *for* now is the one thing that survived the removal — naming every
 //! agent, which is the set a
 //! [`hive_sh4re::permissions::Capability::ManageRootAgent`] holder gets
@@ -28,8 +28,8 @@ pub fn topology_path() -> PathBuf {
     crate::paths::meta_root().join(TOPOLOGY_FILE)
 }
 
-/// On-disk shapes [`read`] accepts. The array is what [`write`] emits; the
-/// map is the pre-#4472 `name → parent | null` format, kept readable so a
+/// On-disk shapes [`read`] accepts. The array is what [`write()`] emits; the
+/// map is the legacy `name → parent | null` format, kept readable so a
 /// hive that upgrades across this change keeps its roster instead of
 /// blanking it until the next `reconcile` pass — and a blank roster is not
 /// a cosmetic gap, it is every `ManageRootAgent` holder losing its mounts
@@ -204,7 +204,7 @@ mod tests {
     }
 
     /// The upgrade path. A hive whose `topology.json` still carries the
-    /// pre-#4472 `name → parent` map must read as the same roster, parent
+    /// legacy `name → parent` map must read as the same roster, parent
     /// values discarded — otherwise the first read after the upgrade hands
     /// `ManageRootAgent` holders an empty mount set.
     #[test]