feat: add timezone settings data export and account deletion

README.md

@@ -217,8 +217,9 @@ production habit data separate from development data.
   server-side; Discord access/refresh tokens are never persisted or sent to React.
 - React detects the browser timezone during initial registration. The server
   validates it using `Intl.DateTimeFormat`, falling back to UTC. Later sign-ins
-  update the Discord profile without changing the saved timezone. A timezone
-  settings UI is deferred; `PATCH /api/me` updates the timezone. Habit timestamps
+  update the Discord profile without changing the saved timezone. **Settings** lets users change their timezone, download a complete JSON export,
+  and permanently delete their account with typed confirmation. `PATCH /api/me`
+  updates the timezone. Habit timestamps
   remain UTC and daily boundaries follow the saved timezone with preserved historical
   deadlines. See the API reference for travel and DST behavior.
 
@@ -325,3 +326,12 @@ Habit tests cover every route, all PRD acceptance behaviors, ownership and Origi
 checks, historical corrections, expiry, timezone boundaries, daily resets, optional
 count carryover, Nivo data adaptation, and migration upgrades. Semantic commits
 separate the database foundation, REST implementation, carryover, and verification.
+
+### Account data
+
+`GET /api/account/export` downloads versioned JSON containing all owned profile,
+habit, revision, dated progress, task, audit, calendar, chart, and delivery records.
+It excludes session tokens and credentials. `DELETE /api/account` requires matching
+Origin and `{ "confirmation": "DELETE" }`; it atomically removes owned records and
+revokes every session. Discord posts and retained operator backups are not erased
+by this action.