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/utils/duration.js

@@ -0,0 +1,16 @@
+// Parses simple duration strings ("30s", "10m", "2h", "1d") to milliseconds.
+// Returns null for anything unparseable. Discord's own timeout API caps at 28
+// days — callers should clamp to MAX_TIMEOUT_MS rather than trust user input.
+const UNIT_MS = { s: 1000, m: 60_000, h: 3_600_000, d: 86_400_000 }
+
+const MAX_TIMEOUT_MS = 28 * 86_400_000
+
+function parseDuration(input) {
+  if (!input) return null
+  const match = /^(\d+)\s*(s|m|h|d)$/i.exec(input.trim())
+  if (!match) return null
+  const [, amount, unit] = match
+  return Number(amount) * UNIT_MS[unit.toLowerCase()]
+}
+
+module.exports = { parseDuration, MAX_TIMEOUT_MS }