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>

client/src/api/client.js

@@ -132,6 +132,10 @@ export const api = {
     createAuthProvider: (data) => req('/admin/auth/providers', { method: 'POST', body: data }),
     updateAuthProvider: (id, data) => req(`/admin/auth/providers/${id}`, { method: 'PUT', body: data }),
     deleteAuthProvider: (id) => req(`/admin/auth/providers/${id}`, { method: 'DELETE' }),
+
+    // ----- Discord bot control (admin only) -----
+    getDiscordBotConfig: () => req('/admin/discord-bot/config'),
+    saveDiscordBotConfig: (data) => req('/admin/discord-bot/config', { method: 'PUT', body: data }),
   },
 }