Add Discord bot (moderation, filters, scheduling, roles, invites, site integration)

Standalone bot/ service (its own package.json/Dockerfile) managed entirely
through a new admin-only Discord Bot panel — token stored encrypted in the
DB and pushed to the bot process in-memory, never an env var. Built in
phases, each independently verified against a live Discord guild:

- Bot skeleton: gateway connection, internal shared-secret API, self-heals
  on its own restart by pulling config from the site
- Moderation core: /ban /kick /mute /warn /warnings + mod-log channel
- Word/invite/spam filtering with leetspeak-resistant normalization and a
  staff role/channel allowlist
- Scheduled messages: recurring (cron) and one-off channel posts
- Role assignment: button role menus, auto-role on join, temp roles,
  bulk role ops
- Auto-rotating primary invite with an audit log
- Site integration: news-publish -> Discord announce webhook, manual
  /announce, read-only /wiki search

Also fixes a pre-existing bug in both DB pools (server + bot): the mariadb
driver defaulted to timezone 'local', silently mis-serializing bound Date
params by the host's local offset instead of the DB's UTC session.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bot/src/model/tempRoles.js

@@ -0,0 +1,26 @@
+const db = require('../db')
+
+// Upsert — re-granting the same temp role refreshes its expiry instead of
+// creating a duplicate row (see UNIQUE(guild,user,role) in schema.sql).
+async function add({ guildId, userId, roleId, expiresAt, createdBy }) {
+  await db.query(
+    `INSERT INTO temp_roles (guild_id, user_id, role_id, expires_at, created_by)
+     VALUES (?, ?, ?, ?, ?)
+     ON DUPLICATE KEY UPDATE expires_at = VALUES(expires_at), created_by = VALUES(created_by)`,
+    [guildId, userId, roleId, expiresAt, createdBy || null],
+  )
+}
+
+async function remove(guildId, userId, roleId) {
+  await db.query('DELETE FROM temp_roles WHERE guild_id = ? AND user_id = ? AND role_id = ?', [guildId, userId, roleId])
+}
+
+async function listExpired() {
+  return db.query('SELECT id, guild_id, user_id, role_id FROM temp_roles WHERE expires_at <= NOW()')
+}
+
+async function removeById(id) {
+  await db.query('DELETE FROM temp_roles WHERE id = ?', [id])
+}
+
+module.exports = { add, remove, listExpired, removeById }