Add uo-link sidecar foundation: config store + REST client (phase 0)

Introduces the DB-backed connection config for the uo-link sidecar (the
HTTP + WebSocket bridge to the ServUO shard) and a never-throw REST client,
mirroring the existing Discord-bot integration:

- uo_link_config singleton table (base/ws URL, AES-256-GCM-encrypted shared
  token, protocol pin, enabled, and last-known status/plugin_connected/
  last_event_at/boot_id mirrors for the admin panel).
- model/uoLinkConfig: getSafe (never returns the token — only hasToken),
  getWithToken (server-side decrypt), save (blank token = unchanged),
  recordStatus (mirror the sidecar's reported state).
- utils/uoLinkClient: never-throw fetch client returning {ok,data,status,
  error}; Bearer token + X-UOLink-Version on every call; brief config cache;
  helpers for health/char/roster/vendors/history/economy/link/towncrier.
- .env.example: UOLINK_BASE_URL/WS_URL/PROTOCOL defaults (token stays
  admin-managed in the DB, never an env var).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011qPmpmVH1xGCiZoz9m9vW3

server/src/model/uoLinkConfig/uoLinkConfig.db.js

@@ -0,0 +1,28 @@
+const { query } = require('../../utils/db')
+
+const COLS =
+  'id, base_url, ws_url, auth_token_enc, protocol, enabled, status, status_detail, plugin_connected, last_event_at, boot_id, updated_by, created_at, updated_at'
+
+// Singleton row (id = 1). Returns null until the admin saves it for the first time.
+async function get() {
+  const rows = await query(`SELECT ${COLS} FROM uo_link_config WHERE id = 1 LIMIT 1`)
+  return rows[0] || null
+}
+
+// Upsert the singleton row. `fields` are column values already prepared by the
+// model (token pre-encrypted). Only the provided columns are written/updated.
+async function upsert(fields) {
+  const cols = Object.keys(fields)
+  const vals = cols.map((c) => fields[c])
+  const insertCols = ['id', ...cols].map((c) => `\`${c}\``).join(', ')
+  const placeholders = ['1', ...cols.map(() => '?')].join(', ')
+  const updates = cols.map((c) => `\`${c}\` = VALUES(\`${c}\`)`).join(', ')
+  await query(
+    `INSERT INTO uo_link_config (${insertCols}) VALUES (${placeholders})
+     ON DUPLICATE KEY UPDATE ${updates}`,
+    vals,
+  )
+  return get()
+}
+
+module.exports = { get, upsert }