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/dashboard_events.rs

@@ -165,10 +165,7 @@ pub enum DashboardEvent {
     /// last one cached on the coordinator. Mutation sites (lifecycle
     /// endpoints, `actions::destroy` / approve, `crash_watch`'s poll loop)
     /// call the rescan after their work lands.
-    ContainerStateChanged {
-        seq: u64,
-        container: ContainerView,
-    },
+    ContainerStateChanged { seq: u64, container: ContainerView },
     /// A container that was in the previous snapshot is gone. Clients
     /// drop the row by name. Fired alongside any
     /// `nixos-container destroy` (operator-driven or otherwise) on the
@@ -211,12 +208,9 @@ pub enum DashboardEvent {
     /// snapshot-shape rationale as `TombstonesChanged` /
     /// `MetaInputsChanged`: the list is small, snapshot semantics avoid
     /// the add/remove races a per-row event would have, and the
-    /// dashboard's grouping (parent_id) is most naturally re-derived
+    /// dashboard's grouping (`parent_id`) is most naturally re-derived
     /// from the full list.
-    RebuildQueueChanged {
-        seq: u64,
-        queue: Vec<QueueEntry>,
-    },
+    RebuildQueueChanged { seq: u64, queue: Vec<QueueEntry> },
 }
 
 impl DashboardEvent {
@@ -259,13 +253,18 @@ mod tests {
     /// the `kind` JSON field matches `kind_tag()`. The exhaustive
     /// `match` in `kind_tag` already provides compile-time variant
     /// coverage — this test is the value-side guard against
-    /// typos in the snake_case strings vs serde's `rename_all`
+    /// typos in the `snake_case` strings vs serde's `rename_all`
     /// output. `ContainerStateChanged` is omitted from the sample
     /// list only because `ContainerView` has no `Default` impl and
     /// constructing one inline here is more boilerplate than the
     /// test is worth; the variant is still covered by the
     /// `kind_tag` match arm.
     #[test]
+    #[allow(
+        clippy::too_many_lines,
+        reason = "exhaustive coverage of every DashboardEvent variant — the \
+                  length is the point"
+    )]
     fn kind_tag_matches_serde_kind_field() {
         let samples: Vec<DashboardEvent> = vec![
             DashboardEvent::Sent {
@@ -367,11 +366,7 @@ mod tests {
                 .get("kind")
                 .and_then(|k| k.as_str())
                 .expect("kind field present");
-            assert_eq!(
-                ev.kind_tag(),
-                serde_kind,
-                "kind_tag() drift on {ev:?}",
-            );
+            assert_eq!(ev.kind_tag(), serde_kind, "kind_tag() drift on {ev:?}",);
         }
     }
 }