Security: tune the Join Gate, raid mode, anti-nuke and heat with commands

- /security settings, joingate check|account-age, words add|remove|list, raid, antinuke set|limit, heat, alert-dms
- Same rule as the rest of the configuration: owner or trusted, validated in the engine
- schema.sql was missing security_settings.alert_dm, so the bot couldn't read security settings on a database built from it. Fixed, with an ALTER for existing installs
- A test checks every command against Discord's limits

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

docs/database.md

@@ -62,7 +62,7 @@ Every listener **validates the request again**. The dashboard should check that
 
 ## Changing the schema
 
-1. Update `schema.sql`. Use `CREATE TABLE IF NOT EXISTS`, and avoid destructive changes: a bot that is a version behind (or a tool reading the same tables) must keep working against the new schema for a moment. Add a column or table first, and remove old ones in a later release.
+1. Update `schema.sql`. Use `CREATE TABLE IF NOT EXISTS`, and for a new column on an existing table also add `ALTER TABLE ... ADD COLUMN IF NOT EXISTS ...` right after it, so servers set up earlier get the column when they run the file again. Avoid destructive changes: a bot that is a version behind (or a tool reading the same tables) must keep working against the new schema for a moment. Add a column or table first, and remove old ones in a later release.
 2. Add or change the repo method in `internal/db/repos/<area>repo`.
 3. If something outside the bot must make it do something, add a `command_type` to the `CHECK` in the right `*_commands` table and handle it in the listener.
 4. In your pull request, say that the schema changed and whether an existing table is affected, so the maintainer can port the change to the dashboard's migrations.