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]>

schema.sql

@@ -288,6 +288,8 @@ CREATE TABLE IF NOT EXISTS security_settings (
     -- Where alerts go, and who gets pinged for raids and nukes.
     alert_channel_id BIGINT,
     alert_role_id BIGINT,
+    -- Also DM critical alerts to the owner and trusted users.
+    alert_dm BOOLEAN NOT NULL DEFAULT TRUE,
 
     -- Join Gate: checks run on every join, each with its own action.
     joingate_enabled BOOLEAN NOT NULL DEFAULT FALSE,
@@ -348,6 +350,9 @@ CREATE TABLE IF NOT EXISTS security_settings (
     -- Join lockdown (/lockdown joins): every new member is kicked or banned.
     join_lock TEXT NOT NULL DEFAULT 'off' CHECK (join_lock IN ('off', 'kick', 'ban'))
 );
+-- Servers set up before alert_dm existed get it here (CREATE TABLE IF NOT EXISTS
+-- doesn't change an existing table).
+ALTER TABLE security_settings ADD COLUMN IF NOT EXISTS alert_dm BOOLEAN NOT NULL DEFAULT TRUE;
 
 -- Users and roles exempt from anti-nuke, who may also manage its settings.
 -- The server owner is always trusted and never listed here.