clippy: fix lints that crane's cargoClippy properly enforces (#538)

The naersk → crane swap in the parent commit flips clippy from
silently passing to actually failing on `-D warnings` (naersk's
`mode = "clippy"` mangled the `--` separator so the deny never took
effect). This commit clears the surfaced lints so the workspace
builds clean under the new enforcement — every fix is mechanical and
preserves behaviour. Tests still pass (160 across the workspace).

Auto-fixes via `cargo clippy --fix`:
- `doc_markdown` (19 sites): bare identifiers in doc comments
  wrapped in backticks
- `format_in_format_args`, `explicit_into_iter_loop`,
  `redundant_closure_for_method_calls`, `useless_conversion`, and
  a few more — mechanical rewrites of the kind cargo can apply
  safely.

Hand-fixed:
- `match_same_arms` (forge_notify::is_atx_heading): two arms returning
  `true` collapsed into a single `matches!` pattern.
- `cast_sign_loss` + `format_push_string` (mcp.rs status formatter):
  guarded `i64 → u64` through `u64::try_from(…).unwrap_or(0)` (status
  timestamps are always positive in practice; clamp the skew edge to
  0) and swapped `out.push_str(&format!(…))` for `write!` into the
  buffer with an infallible-writer `let _ =`.
- `doc_lazy_continuation` in turn.rs + manager_server.rs + sh4re/lib.rs:
  doc paragraphs that the markdown parser was treating as list-item
  continuations got either a separating blank line or a `/`-for-`+`
  word swap so the parser stops seeing a list.
- `unused_async` (manager_server::handle_request_schedule_prompt):
  function has no `.await`; dropped the `async` and its `.await` call
  site.
- `needless_pass_by_value` (scheduled_prompts::submit): take
  `&NewSchedule` instead of moving the struct in; updated two prod
  callers and eight test sites to pass references.
- `type_complexity` (approvals::mark_cancelled): hoisted the
  7-tuple SELECT row shape into a `type CancelLookupRow = (…);` alias.

Allow-with-reason for intentional patterns:
- `option_option` (6 sites across dashboard / scheduled_prompts /
  manager_server): `Option<Option<T>>` carries three-state PATCH
  semantics (missing key = leave alone, `Some(None)` = clear,
  `Some(Some(v))` = set). Collapsing to `Option<T>` loses the
  "clear" state.
- `dead_code` (rebuild_queue::QueueKind::Destroy /
  QueueSource::CrashRecover; topology::parent_of / default_seed):
  wire-shape variants + API surfaces kept for the upcoming features
  (#361 follow-ups, future `Destroy` queue routing, crash-recovery
  path). Allowed at the variant / function level with the rationale
  in `reason = "…"`.
- `too_many_lines` on three specific call-sites: a 117-line
  exhaustive-variant test (dashboard_events::kind_tag_matches_…),
  the meta-flake string template renderer
  (meta::render_flake_with_lookup), and the notification poll loop
  (forge_notify::poll_once) — splitting any of them would just hide
  the contiguous shape they exist to keep visible.

`nix flake check` formatting target is still broken on main itself
(pre-existing nixfmt drift across ~28 files unrelated to this PR);
left alone here so the scope stays "crane port + lints the port
exposed" and the operator's review doesn't have to triage drive-by
nixfmt churn.

hive-c0re/src/topology.rs

@@ -58,6 +58,11 @@ pub fn read() -> BTreeMap<String, Option<String>> {
 /// or absent from the file. Cheap convenience over `read()` for
 /// callers that want a single entry.
 #[must_use]
+#[allow(
+    dead_code,
+    reason = "convenience API; callers go through `read()` today, kept for the \
+              dashboard/manager-server surfaces landing in #361 follow-ups"
+)]
 pub fn parent_of(name: &str) -> Option<String> {
     read().get(name).cloned().flatten()
 }
@@ -88,10 +93,10 @@ pub fn is_descendant_of(candidate: &str, ancestor: &str) -> bool {
     false
 }
 
-/// Persist the topology map. Sorted JSON output (BTreeMap is sorted by
+/// Persist the topology map. Sorted JSON output (`BTreeMap` is sorted by
 /// key) keeps git diffs minimal across re-writes. Best-effort —
 /// returns an `io::Error` so callers can decide whether a failure
-/// should abort their op (sync_agents, RequestSetParent) or just log.
+/// should abort their op (`sync_agents`, `RequestSetParent`) or just log.
 pub fn write(topology: &BTreeMap<String, Option<String>>) -> std::io::Result<()> {
     let path = topology_path();
     if let Some(parent) = path.parent() {
@@ -111,13 +116,21 @@ pub fn write(topology: &BTreeMap<String, Option<String>>) -> std::io::Result<()>
 /// entries — `sync_agents` only adds rows for newly-spawned agents
 /// against whatever the operator has configured.
 #[must_use]
+#[allow(
+    dead_code,
+    reason = "kept for the dashboard / RequestSetParent write API landing in \
+              #361 follow-ups; `sync_agents` does its own seeding today"
+)]
 pub fn default_seed(agent_names: &[String]) -> BTreeMap<String, Option<String>> {
     let mut out = BTreeMap::new();
     for name in agent_names {
         if name == crate::lifecycle::MANAGER_NAME {
             out.insert(name.clone(), None);
         } else {
-            out.insert(name.clone(), Some(crate::lifecycle::MANAGER_NAME.to_owned()));
+            out.insert(
+                name.clone(),
+                Some(crate::lifecycle::MANAGER_NAME.to_owned()),
+            );
         }
     }
     out
@@ -285,8 +298,8 @@ mod tests {
 
     #[test]
     fn apply_set_parent_refuses_manager_move() {
-        let err =
-            apply_set_parent(&topo_three_level(), crate::lifecycle::MANAGER_NAME, None).unwrap_err();
+        let err = apply_set_parent(&topo_three_level(), crate::lifecycle::MANAGER_NAME, None)
+            .unwrap_err();
         assert!(err.contains("manager"), "err = {err}");
     }