feat(brand): BRAND_* env scheme — instance branding without a rebuild

Replace baked-in UOM/MysticMoon/UOMysticmoon branding with a BRAND_* env
scheme so one prebuilt image runs as any shard; UOMysticmoon becomes the
first tenant that sets these vars rather than a special case in the code.

Architecture (chosen because the app ships as a prebuilt image):
- server/src/config/brand.js + bot/src/brand.js read BRAND_* once at boot,
  with Runic Gateway defaults.
- Text/colors reach the SPA at RUNTIME through the existing public settings
  API (settings.model.getPublic -> SiteContext), so no client rebuild. The
  admin-editable site title + contact email still override BRAND_NAME/email.
- SiteContext applies BRAND_ACCENT_COLOR to the --accent CSS var at runtime.
- Express templates the built index.html <title>/description/OG/favicon at
  serve time from BRAND_* (renderIndexHtml in app.js).
- Server-side consumers read brand directly: emails, TOTP issuer, API docs,
  boot logs, HTML error page. Bot uses it for embed color + logs.

Assets: logo/hero/favicon delivered from a ./brand:/app/brand bind-mount
(BRAND_LOGO/HERO/FAVICON), with neutral defaults baked in; hero falls back
to a built-in image when unset.

Scope: also genericized package.json names (uomysticmoon-* -> runic-gateway-*)
and the DB_NAME/DB_USER/COOKIE_NAME code defaults (runic_gateway/runic/
rg_token). Production keeps its real values by pinning them in .env — see
.env.uomysticmoon.example, which reproduces the exact UOMysticmoon identity
(proof the substitution works). Changing a deployed COOKIE_NAME invalidates
existing sessions, so UOMysticmoon pins uomm_token.

Verified: 193 server tests pass, client builds, app.js loads + templates the
built index.html, brand transform injects title/description/OG/favicon.

server/db/seed.js

@@ -4,6 +4,7 @@ const settingsDb = require('../src/model/settings/settings.db')
 const wikiDb = require('../src/model/wiki/wiki.db')
 const users = require('../src/model/users/users.model')
 const { ensureSchema, close } = require('../src/utils/db')
+const brand = require('../src/config/brand')
 
 const log = require('../src/utils/logger')('seed')
 
@@ -13,20 +14,20 @@ const DEFAULT_SETTINGS = {
   site_mode_changed_at: '',
   site_mode_changed_by: '',
   maintenance_message:
-    'Mysticmoon is being shaped beneath a midnight sky. The site will return soon.',
+    `${brand.shortName} is being shaped beneath a midnight sky. The site will return soon.`,
   status_message: 'In progress.',
   homepage_teaser:
-    'Mysticmoon is still being shaped beneath a midnight sky. A quiet preview for ' +
+    `${brand.shortName} is still being shaped beneath a midnight sky. A quiet preview for ` +
     'future news, screenshots, guides, and community notes as the world comes online.',
-  contact_email: process.env.CONTACT_TO || 'UOMysticmoon@gmail.com',
-  site_title: 'UOMysticmoon',
+  contact_email: brand.contactEmail,
+  site_title: brand.name,
 }
 
 // Starter wiki sections (editable later via the admin panel).
 // [slug, title, description, sort_order]
 const WIKI_CATEGORIES = [
   ['guides', 'Guides', 'Getting started and how-to guides.', 10],
-  ['world', 'World & Lore', 'Regions, maps, and the story of Mysticmoon.', 20],
+  ['world', 'World & Lore', `Regions, maps, and the story of ${brand.shortName}.`, 20],
   ['gameplay', 'Systems & Gameplay', 'Mechanics, items, monsters, and crafting.', 30],
   ['community', 'Community & Rules', 'Player conduct and shard policies.', 40],
 ]