Add per-staff metrics: StaffAction event log + /stats command

Event-sourced tracking of staff/ticket lifecycle actions, plus a /stats
command. Foundation for a future tickets-website analytics dashboard.

Data:
- StaffAction model (event log) + Ticket.game / Ticket.closedAt
- STATS_ADMIN_IDS config (who may view others' stats)

Recording (fire-and-forget, idempotent on real state transitions):
- claim, response (channel reply + /response send), escalate, de-escalate,
  transfer, close (4 sites), reopen — each denormalizes ticketType, tier,
  priority, game, requester (senderEmail / creatorId), guildId
- close events carry closerType / resolverId (claimer credit) / wasClaimed;
  transfer carries fromId / toId; reopen stamps resolverId
- conditional close transition helper (atomic open->closed + closedAt) shared
  by all four close paths

Query + command:
- pure period parser (presets + free-text) and stats shaper (per-metric keys)
- command-aware autocomplete dispatch
- /stats: period (autocomplete) + member (admin-gated) + source (all/email/
  discord), ManageMessages + staff-role gated, ephemeral, tier-labeled embed

288+ unit tests; timing/busiest-times data is collected but displayed later.

services/staffStats.js

@@ -0,0 +1,54 @@
+'use strict';
+
+const mongoose = require('mongoose');
+const { logError } = require('./debugLog');
+
+// Derives ticketType from gmailThreadId prefix.
+// discord-* and discord-msg-* → 'discord'; everything else → 'email'.
+function deriveTicketType(gmailThreadId) {
+  if (!gmailThreadId) return 'email';
+  if (gmailThreadId.startsWith('discord-')) return 'discord';
+  return 'email';
+}
+
+// Extracts the standard event fields from a ticket document.
+// Returns a plain object — does NOT include guildId (call-site only).
+function denormalizeTicket(ticket) {
+  if (!ticket) return {};
+  return {
+    ticketType:    deriveTicketType(ticket.gmailThreadId),
+    tier:          ticket.escalationTier ?? 0,
+    priority:      ticket.priority,
+    game:          ticket.game,
+    senderEmail:   ticket.senderEmail,
+    creatorId:     ticket.creatorId,
+    gmailThreadId: ticket.gmailThreadId
+  };
+}
+
+// recordAction(staffId, type, payload)
+//
+// payload may carry:
+//   ticket  — a Ticket doc to denormalize standard fields from
+//   guildId — must come from the call site (not on the Ticket schema)
+//   any other StaffAction field — these override denormalized values
+//
+// Fire-and-forget: never throws, never blocks the caller.
+// The outer try/catch catches synchronous errors (e.g. model not registered
+// during early boot); the inner .catch handles async DB rejections.
+function recordAction(staffId, type, payload) {
+  try {
+    const { ticket, ...overrides } = payload || {};
+    const base = denormalizeTicket(ticket);
+    const doc = { staffId, type, ...base, ...overrides };
+
+    const StaffAction = mongoose.model('StaffAction');
+    StaffAction.create(doc).catch(err => {
+      logError('staffStats.recordAction', err);
+    });
+  } catch (err) {
+    logError('staffStats.recordAction', err);
+  }
+}
+
+module.exports = { recordAction, denormalizeTicket, deriveTicketType };