feat(server): port the UO models, utils and schema fragment

The data half of the extraction: 8 model directories, 13 utils, the shard
stream catalog and the 27-table schema fragment with its purge.

server/core.js is what makes the port a one-line import change per file rather
than a signature change per function. Ported code requires its dependencies at
file scope -- `const { query } = require('../../core')` -- which runs before
register() has been called and before any ctx exists. So every member is a
stable function that resolves ctx when CALLED, and nothing may be destructured
off ctx at init either, because core is free to hand over a getter.

Two helpers are vendored rather than taken from ctx, and the line between them
is the point. utils/excerpt.js is core's deriveExcerpt -- nine lines of pure
text handling. Core's sanitiser next to it was NOT copied: a second copy of a
security control diverges silently the moment either is fixed. announceLinks.js
vendors legError and articleUrl the same way, but baseUrl could not be: core's
reads APP_BASE_URL, and §2.7 forbids a module reading core's environment, so it
comes off ctx.site.baseUrl.

The schema fragment is core's 27 shard_*/uo_link_* statements, verbs CREATE,
ALTER and UPDATE only, every CREATE TABLE guarded. Two of its tables carry a
foreign key INTO users, which is allowed and is why the replay order matters --
core's schema is in place before this runs. The reverse never occurs and must
not: it would make core unable to boot without a module installed.

One real port bug caught by the integration run, not by tests: the atlas art
map resolved `../../../db/data`, which pointed at core's tree when this file
lived there and points outside server/ now. A path that happens to resolve is
exactly what survives a green suite, because the absent-file branch returns {}
and looks like the normal case.

Co-Authored-By: Claude <noreply@anthropic.com>

server/model/shardLinks/shardLinks.model.js

@@ -0,0 +1,37 @@
+// Site-side mirror of in-game-account → website-user links. The sidecar owns the
+// authoritative link (it tags the game account on /link/confirm); this model
+// records it locally so the player portal can list links and enforce ownership.
+
+const db = require('./shardLinks.db')
+
+function toSafe(row) {
+  if (!row) return null
+  return {
+    account: row.account,
+    userId: row.user_id,
+    charName: row.char_name || null,
+    linkedAt: row.linked_at,
+  }
+}
+
+async function link({ account, userId, charName }) {
+  return toSafe(await db.upsert({ account, userId, charName }))
+}
+
+async function listForUser(userId) {
+  const rows = await db.listByUser(userId)
+  return rows.map(toSafe)
+}
+
+const ownsAccount = (account, userId) => db.isOwnedBy(account, userId)
+
+async function getByAccount(account) {
+  return toSafe(await db.getByAccount(account))
+}
+
+const unlink = (account, userId) => db.remove(account, userId)
+
+// Drop the local mirror for an account (source-of-truth severed elsewhere).
+const removeByAccount = (account) => db.removeByAccount(account)
+
+module.exports = { link, listForUser, ownsAccount, getByAccount, unlink, removeByAccount }