docs(website): plan self-service account deletion

ACCOUNT_DELETION.md is the plan of record for the org lead's decision:
a member deletes their own account on the website and in the app, as
Google Play requires of an app that starts accounts.

- One deletion service for the admin route and the member's own route,
  with a confirm step, the last-admin and demo refusals, clearing the
  username snapshots on what the member wrote, and a notice by email.
- MODULE_API 1.20.0: api.onUserDeleted, which runs after the commit and
  can't stop a deletion.
- Screens on the web and in the app; runicgateway.com /delete-account/
  as the address Play is given.
- What the schema already does (59 keys: credentials cascade, content
  detaches), the gaps, six questions, and the build order.

M8's order puts account deletion before report, block and hide, which
moves USER_SAFETY.md's reportTargets to MODULE_API 1.21.0.

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

README.md

@@ -37,7 +37,8 @@ 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 |
-| [USER_SAFETY.md](website/USER_SAFETY.md) | **Plan, 2026-10-29** — report, block and hide on the website and in the app: an account-wide block, a member's own hide and staff's hide for everyone, with module-owned report targets (`MODULE_API` 1.20.0) |
+| [ACCOUNT_DELETION.md](website/ACCOUNT_DELETION.md) | **Plan, 2026-10-29**: a member deletes their own account on the website and in the app, as Google Play requires. One deletion service for staff and self, an `onUserDeleted` module hook (`MODULE_API` 1.20.0), and runicgateway.com's `/delete-account/` page as the address Play is given |
+| [USER_SAFETY.md](website/USER_SAFETY.md) | **Plan, 2026-10-29** — report, block and hide on the website and in the app: an account-wide block, a member's own hide and staff's hide for everyone, with module-owned report targets (`MODULE_API` 1.21.0, after account deletion) |
 | [DEMO_MODE.md](website/DEMO_MODE.md) | **Design, fully decided 2026-10-23** — 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 |