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.

client/src/routes/admin/AdminLayout.jsx

@@ -126,7 +126,7 @@ const navBtnBase = {
 
 export default function AdminLayout() {
   const { user, logout } = useAuth()
-  const { mode } = useSite()
+  const { mode, siteTitle } = useSite()
   const navigate = useNavigate()
   const location = useLocation()
   const title =
@@ -225,7 +225,7 @@ export default function AdminLayout() {
           <MoonDot />
           <div>
             <div className="display" style={{ fontSize: '1.02rem', color: 'var(--head)', letterSpacing: '0.03em' }}>
-              UOMysticmoon
+              {siteTitle}
             </div>
             <div className="sans" style={{ color: 'var(--dim)', fontSize: '0.66rem', letterSpacing: '0.14em', textTransform: 'uppercase' }}>
               Admin

client/src/routes/admin/AdminLogin.jsx

@@ -3,6 +3,7 @@ import { Link, useNavigate, useLocation } from 'react-router-dom'
 import MoonDot from '../../components/MoonDot.jsx'
 import ProviderIcon from '../../components/ProviderIcon.jsx'
 import { useAuth } from '../../contexts/AuthContext.jsx'
+import { useSite } from '../../contexts/SiteContext.jsx'
 import { api } from '../../api/client.js'
 
 // Friendly copy for the ?sso_error codes the SSO callback can redirect back with.
@@ -15,9 +16,6 @@ const SSO_ERRORS = {
   error: 'Could not complete sign-in. Please try again.',
 }
 
-const BG =
-  "linear-gradient(180deg,rgba(11,15,20,0.72),rgba(11,15,20,0.9)),url('/assets/img/uomysticmoon-main-hero.png')"
-
 // Hidden anti-bot field. Off-screen via CSS (NOT display:none/hidden, which bots
 // skip) so real users never fill it but naive scripted bots do. Name must match
 // the server's HONEYPOT_FIELD ('company').
@@ -33,6 +31,8 @@ const honeypotStyle = {
 
 export default function AdminLogin() {
   const { user, login, loginTotp, ssoLoginTotp } = useAuth()
+  const { siteTitle, heroImage } = useSite()
+  const BG = `linear-gradient(180deg,rgba(11,15,20,0.72),rgba(11,15,20,0.9)),url('${heroImage}')`
   const navigate = useNavigate()
   const location = useLocation()
   const dest = location.state?.from?.pathname || '/admin'
@@ -160,7 +160,7 @@ export default function AdminLogin() {
             <MoonDot size={15} glow={0.55} />
           </div>
           <h1 className="display" style={{ margin: 0, fontSize: '1.7rem', letterSpacing: '0.04em', color: 'var(--head)' }}>
-            UOMysticmoon
+            {siteTitle}
           </h1>
           <p className="sans" style={{ margin: '6px 0 0', color: '#9aa6b4', fontSize: '0.8rem', letterSpacing: '0.16em', textTransform: 'uppercase' }}>
             Admin Panel

client/src/routes/admin/views/EmailDelivery.jsx

@@ -1,5 +1,6 @@
 import { useCallback, useEffect, useState } from 'react'
 import { api } from '../../../api/client.js'
+import { useSite } from '../../../contexts/SiteContext.jsx'
 
 // Email delivery panel (Gmail over OAuth2), rendered as a section on the Settings
 // page. Sending is authorized by an in-app "Connect Gmail" consent flow that
@@ -52,6 +53,7 @@ function StatusPanel({ config }) {
 }
 
 export default function EmailDelivery() {
+  const { siteTitle } = useSite()
   const [config, setConfig] = useState(null)
   const [error, setError] = useState('')
   const [senderName, setSenderName] = useState('')
@@ -213,7 +215,7 @@ export default function EmailDelivery() {
               onChange={(e) => setSenderName(e.target.value)}
               className="input"
               autoComplete="off"
-              placeholder="UOMysticmoon"
+              placeholder={siteTitle}
             />
           </label>