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-sh4re/src/lib.rs

@@ -752,14 +752,10 @@ pub enum ManagerRequest {
     Status,
     /// Operator-injected message TO the manager (from the manager's own web
     /// UI). Same shape as `AgentRequest::OperatorMsg`.
-    OperatorMsg {
-        body: String,
-    },
+    OperatorMsg { body: String },
     /// Last `limit` messages addressed to the manager, newest-first.
     /// Non-mutating; mirror of `AgentRequest::Recent`.
-    Recent {
-        limit: u64,
-    },
+    Recent { limit: u64 },
     /// Initialise a brand-new agent's proposed config repo and queue an
     /// approval for the operator to review. On approval hive-c0re seeds
     /// `/agents/<name>/config/` with the default `agent.nix` template,
@@ -776,23 +772,15 @@ pub enum ManagerRequest {
         description: Option<String>,
     },
     /// Stop a sub-agent (graceful).
-    Kill {
-        name: String,
-    },
+    Kill { name: String },
     /// Start a previously-stopped sub-agent container.
-    Start {
-        name: String,
-    },
+    Start { name: String },
     /// Restart a sub-agent container (stop + start).
-    Restart {
-        name: String,
-    },
+    Restart { name: String },
     /// Rebuild a sub-agent: re-applies the current hyperhive flake +
     /// agent.nix, restarts the container. No approval required —
     /// it's idempotent and the manager owns its own update cadence.
-    Update {
-        name: String,
-    },
+    Update { name: String },
     /// Submit a config commit for the user to approve. `commit_ref` must
     /// be a commit sha (7-40 hex chars, short or full) in the agent's
     /// proposed config repo — a branch or tag name is rejected so the