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/roles/tempRoleSweeper.js

@@ -0,0 +1,48 @@
+// Once-a-minute sweep for expired temp_roles: removes the Discord role (best
+// effort — the member/guild/role may already be gone) then deletes the row
+// regardless, so a stale row can never block future re-grants of the same
+// role to the same member.
+const cron = require('node-cron')
+
+const tempRoles = require('../model/tempRoles')
+const createLogger = require('../utils/logger')
+
+const log = createLogger('temproles')
+
+let client = null
+let task = null
+
+async function sweep() {
+  try {
+    const expired = await tempRoles.listExpired()
+    for (const row of expired) {
+      try {
+        const guild = await client.guilds.fetch(row.guild_id)
+        const member = await guild.members.fetch(row.user_id).catch(() => null)
+        if (member) await member.roles.remove(row.role_id).catch(() => {})
+      } catch (err) {
+        log.warn('failed to remove expired temp role', { message: err.message, roleId: row.role_id, userId: row.user_id })
+      } finally {
+        await tempRoles.removeById(row.id)
+      }
+    }
+  } catch (err) {
+    log.error('temp role sweep failed', { message: err.message })
+  }
+}
+
+function start(discordClient) {
+  client = discordClient
+  task = cron.schedule('* * * * *', sweep)
+  log.info('temp role sweeper started')
+}
+
+function stop() {
+  if (task) {
+    task.stop()
+    task = null
+  }
+  client = null
+}
+
+module.exports = { start, stop }