feat(docs): phase 16 - the RunicNPC subgroup, its API carried in full and drift-checked

PLAN.md §16 phase 16, with the org lead's D72-D74 (count of record 74).

- Eight pages nested in the Rust group at /docs/rust/runicnpc/ (D72): the
  overview, Install RunicNPC, Commands, NPC profiles, NPC placements, Cost and
  caps, Profile fields (the one field reference the editor, rnpc.profile set,
  the data file and the API all share) and The API.
- The API page carries every call, hook and data shape (D62), in the site's
  own words, with no decision numbers and no per-call version history (D74).
  Signatures print from src/data/runicnpc.mjs through Signature.astro.
- checkReference.mjs gains two sections. Against docs main:runicnpc/API.md:
  the API version, 24 call and 10 hook signatures, and the field names of the
  profile, RunicNpc_List rows, placements, routes and owners (D73), plus
  exactly one <Signature> per call on api.mdx. Against runicnpc-rust
  main:plugin/RunicNPC.cs: console verbs, permissions, place options and
  config keys. Six planted drifts all failed before it was trusted.
- checkSidebar and checkTerms read nested sidebar groups via flatLabels().
- The Rust overview, Events zones and rewards, and Canonical documents link
  the new pages; the canonical documents gain the four runicnpc/ docs.

Both NPC admin screens were walked on the walk site first (D36); nothing was
saved. npm run verify is green.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

scripts/checkSidebar.mjs

@@ -22,13 +22,15 @@
  * No token and no network: both trees are in this repository.
  */
 
-import { docsSidebar, plannedSidebar } from '../src/config/sidebar.mjs';
+import { docsSidebar, plannedSidebar, flatLabels } from '../src/config/sidebar.mjs';
 
 const failures = [];
 const fail = (what, detail) => failures.push({ what, detail });
 
-const live = new Map(docsSidebar.map((g) => [g.label, g.items.map((i) => i.label)]));
-const planned = new Map(Object.entries(plannedSidebar));
+// A nested group (RunicNPC inside Rust, phase 16) flattens to `Group › Page` labels, so its
+// pages and their order are held to the plan exactly as a top-level group's are.
+const live = new Map(docsSidebar.map((g) => [g.label, flatLabels(g.items)]));
+const planned = new Map(Object.entries(plannedSidebar).map(([label, items]) => [label, flatLabels(items)]));
 
 // ── Groups ──────────────────────────────────────────────────────────────────
 for (const label of live.keys()) {