feat(docs): phase 14 - game-neutral core docs, an Ultima Online group, and checkTerms

PLAN.md §16, D63/D64, plus D67-D69 taken 2026-10-22.

- Core docs use core's words: a Team, a game server, the sidecar, the bridge
  plugin, the game module. Detail that belonged to Ultima Online moved into
  its pages rather than being dropped.
- New "Ultima Online" sidebar group (nine pages): an overview, Connect a
  ServUO shard, Verify the bridge, The shard connection, Client files,
  Troubleshooting, Bridge.cfg, sidecar.toml, Shard event catalog. Five moved
  URLs answer a real 301 (src/config/redirects.mjs, asserted by the served
  test).
- Getting started is game-neutral. "Connect your game server" keeps the old
  URL and hands off to each game; Rust links docs main:rust-link/INSTALL.md
  until phase 15. "Verify the whole stack" stays, neutral (D69).
- D68: GameExample.astro labels a game's real example on a core page with the
  game's name; checkTerms allows that game's words inside it.
- scripts/checkTerms.mjs, the twelfth check: 16 game words, docs pages and
  both sidebar trees, one allowlisted phrase (Discord's "Guild (server) ID").
  Wired into verify and pr-checks.yml.
- canonicalDocs grouped by game; the Rust group carries four documents.
- D67: the screenshot rule from #32 is adopted.

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

scripts/checkReference.mjs

@@ -168,7 +168,7 @@ async function run() {
   //
   // Existence only. A link to a document that moved is the single most likely way this
   // section breaks, and it is exactly what a build can answer.
-  for (const docPath of Object.keys(canonicalDocs)) {
+  for (const docPath of Object.values(canonicalDocs).flatMap((group) => Object.keys(group))) {
     const url = `${BASE}/api/v1/repos/${ORG}/docs/contents/${docPath}?ref=main`;
     const res = await fetch(url, { headers: { Authorization: `token ${TOKEN}` } });
     if (res.ok) ok(`canonical doc ${docPath}`);