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.

docs/web-ui/dashboard.md

@@ -59,8 +59,8 @@ surfaces, not tab panes.
 **C0NTAINERS** — live containers rendered as a flat,
 alphabetically-sorted list. The renderer still walks
 `ContainerView.parent` for a depth-first tree with ASCII glyphs
-(`├─`, `└─`, `│  ` continuation columns), but #4472 removed that field,
-so every row sits at depth 0 and the renderer paints no glyph. The tree
+(`├─`, `└─`, `│  ` continuation columns), but that field no longer
+exists, so every row sits at depth 0 and the renderer paints no glyph. The tree
 sorts alphabetically;
 roots likewise. The tree tolerates cycles in the parent graph —
 it appends orphaned containers (not reachable from any root)
@@ -981,7 +981,7 @@ identically.)
 
 ### Topology tree
 
-⚠️ **Dormant since #4472,** which removed `ContainerView.parent`:
+⚠️ **Dormant now that `ContainerView.parent` no longer exists:**
 `buildAgentTree` now puts every container at depth 0 and the rules below are
 all no-ops — the list renders flat. The walk and the prefix painting are
 still in `swarm.js`; retiring them falls to the frontend owner rather
@@ -1032,8 +1032,8 @@ frosted-mauve bar slides up from the bottom of the viewport
   - `DESTR0Y` / `PURG3` — always available
 <!-- vale write-good.Passive = YES -->
 
-  #4472 removed the `M0V3` picker that used to sit here — an agent has
-  no parent to move it to any more.
+  The `M0V3` picker that used to sit here no longer exists — an agent
+  has no parent to move it to any more.
 - **`✕ clear`** button + `Esc` key clear the entire selection.
 
 Every render prunes stale selections (agents destroyed while