Help and docs for the new commands

- /help is sent as a few messages (Discord caps an embed at 6000 characters), with a test for the limits
- command reference, features, self-hosting, beta and getting-started pages describe the commands; the SQL section is gone
- development and contributing: every setting needs a command

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

CONTRIBUTING.md

@@ -44,6 +44,7 @@ These are the things a reviewer will check first. The reasons are in the [Develo
 - **Check permissions in the handler.** `DefaultMemberPermissions` only hides a command from the menu.
 - **No SQL outside repos.** Always use query parameters (`$1`), never string formatting.
 - **A module that acts on a server starts off.** An admin turns it on.
+- **Every setting has a command.** The bot works fully without a dashboard, so a setting must be visible and changeable with slash commands.
 - **Escape user text and set `AllowedMentions`** so a message can't ping people.
 - **Validate everything that comes from users or from other programs writing to the database**: options, custom IDs, command payloads.
 - **No secrets** in code, logs, tests or commit messages.