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>

package.json

@@ -6,9 +6,11 @@
   "scripts": {
     "install-server": "npm install --prefix server",
     "install-client": "npm install --prefix client",
-    "install-all": "npm run install-server && npm run install-client",
+    "install-bot": "npm install --prefix bot",
+    "install-all": "npm run install-server && npm run install-client && npm run install-bot",
     "server": "npm run dev --prefix server",
     "client": "npm run dev --prefix client",
+    "bot": "npm run dev --prefix bot",
     "seed": "npm run seed --prefix server",
     "build": "npm run build --prefix client",
     "start": "npm start --prefix server"