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.

.env.example

@@ -1,5 +1,7 @@
-# ─── UOMysticmoon — root environment (used by docker-compose) ───
+# ─── Runic Gateway — root environment (used by docker-compose) ───
 # Copy to .env and fill in. NEVER commit the real .env.
+# To run this as an existing branded instance (e.g. UOMysticmoon), see
+# .env.uomysticmoon.example for the exact BRAND_*/DB pinning to copy in.
 
 # Container image tag pulled by docker-compose (app + bot). Published by the
 # Gitea Actions workflow on every merge to main as `latest` and `sha-<7>`.
@@ -23,12 +25,32 @@ LOG_TO_FILE=true        # set false for console-only
 LOG_DIR=/app/logs       # log directory inside the container (bind-mounted to ./logs)
 LOG_FILE=app.log
 
+# ─── Branding (BRAND_*) ───────────────────────────────────────────────────
+# Instance identity. Defaults render as "Runic Gateway"; set these to rebrand
+# without a rebuild. Text + colors reach the SPA through the settings API at
+# runtime; the server templates index.html <title>/meta/OG/favicon at boot. The
+# admin-editable "site title" and "contact email" settings, if set, override
+# BRAND_NAME / BRAND_CONTACT_EMAIL.
+BRAND_NAME=Runic Gateway
+BRAND_SHORT_NAME=Runic Gateway
+BRAND_TAGLINE=an independent private Ultima Online shard
+BRAND_DESCRIPTION=Runic Gateway — an independent private Ultima Online shard. News, screenshots, guides, and community notes.
+BRAND_CONTACT_EMAIL=
+BRAND_URL=
+# Accent color — drives the web theme's --accent and the Discord embed color.
+BRAND_ACCENT_COLOR=#7f99bd
+# Image assets: paths under the /brand mount (see docker-compose.yml) or absolute
+# URLs. Blank = built-in defaults (hero falls back to a neutral built-in image).
+BRAND_LOGO=
+BRAND_HERO=
+BRAND_FAVICON=
+
 # Database (the values here are shared by the `db`, `app`, and `bot` containers —
 # the bot only ever touches its own tables: guild_config, mod_actions, warnings)
 DB_HOST=db
 DB_PORT=3306
-DB_NAME=uomysticmoon
-DB_USER=uomm
+DB_NAME=runic_gateway
+DB_USER=runic
 DB_PASSWORD=change-me-db-password
 DB_ROOT_PASSWORD=change-me-root-password
 
@@ -38,7 +60,8 @@ JWT_EXPIRES_IN=1d
 # auto = Secure cookie only when the request arrives over HTTPS (Pangolin).
 # Leave as auto so login works both via the LAN IP (HTTP) and the proxy (HTTPS).
 COOKIE_SECURE=auto
-COOKIE_NAME=uomm_token
+# Changing this on a live instance invalidates existing sessions (users re-login).
+COOKIE_NAME=rg_token
 
 # Reverse-proxy trust (req.ip / req.secure for rate limiting, backoff, bot-ban).
 # Path: client -> Pangolin -> newt agent "ptero" (separate VM) -> app. Pin this
@@ -51,8 +74,8 @@ TRUST_PROXY=1
 # request (to verify/refresh ptero's IP without redeploying). Noisy; keep off.
 DEBUG_TRUST_PROXY=0
 
-# Optional TOTP two-factor (opt-in per user).
-TOTP_ISSUER=UOMysticmoon
+# Optional TOTP two-factor (opt-in per user). Defaults to BRAND_NAME when unset.
+# TOTP_ISSUER=Runic Gateway
 TOTP_CHALLENGE_TTL=5m
 
 # First admin bootstrap — created only if no users exist yet.