docs(website): design demo mode for demo.runicgateway.com

The design for website#222, before any code: one DEMO_MODE flag on the
normal image that locks destructive writes with a 403 DEMO_LOCKED, four
published static logins, no outbound mail/push/Discord, a banner with the
next reset time, and a scheduled wipe on the demo-site runner (drop the
volumes, redeploy, seed accounts + the rig link + content).

Tier A locks are listed route by route. Nine questions for the org lead
(module lock declaration, the rig, visitor content, rig sharing with
walks, the stand-in Steam link, cadence, where the files live, version).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

README.md

@@ -37,6 +37,7 @@ sidecar as a service, and hands you the values the website needs.
 | [SHARD_VISIBILITY.md](website/SHARD_VISIBILITY.md) | Who sees which shard data — the admin-configurable audience framework |
 | [TRUSTED_DEVICES_MFA.md](website/TRUSTED_DEVICES_MFA.md) | TOTP two-factor, trusted devices and recovery codes |
 | [STEAM_SIGNIN.md](website/STEAM_SIGNIN.md) | **Plan, built 2026-10-19** — Sign in with Steam as a built-in provider beside Google and Discord (OpenID 2.0), and a Steam id for modules |
+| [DEMO_MODE.md](website/DEMO_MODE.md) | **Design, awaiting answers** — the public `demo.runicgateway.com`: one flag that locks destructive actions, static logins, and a wipe every couple of hours (website#222) |
 | [MODERATION_APPEALS.md](website/MODERATION_APPEALS.md) | Moderation actions, content reports and the appeals flow |
 | [SPAWN_ATLAS.md](website/SPAWN_ATLAS.md) | The bestiary / spawn atlas: what the shard contains, parsed from the shard's own ServUO files — served over the bridge since Protocol 8, so no shared filesystem |
 | [CLILOCS.md](website/CLILOCS.md) | UO's id → name table, so items have names. The shard decompresses and serves it over the bridge; the desktop conversion it replaced is gone |