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.

handlers/commands/response.js

@@ -17,6 +17,7 @@ const { mongoose } = require('../../db-connection');
 const { CONFIG } = require('../../config');
 const { replaceVariables } = require('../../utils');
 const { logError } = require('../../services/debugLog');
+const { recordAction } = require('../../services/staffStats');
 
 const Tag = mongoose.model('Tag');
 const Ticket = mongoose.model('Ticket');
@@ -38,14 +39,18 @@ async function handleResponse(interaction) {
   }
 }
 
-async function handleResponseSend(interaction) {
+async function handleResponseSend(interaction, _TagModel, _TicketModel, _recordAction) {
+  const TTag = _TagModel || Tag;
+  const TTicket = _TicketModel || Ticket;
+  const record = _recordAction || recordAction;
+
   const name = interaction.options.getString('name');
-  const tag = await Tag.findOne({ name }).lean();
+  const tag = await TTag.findOne({ name }).lean();
   if (!tag) {
     return interaction.reply({ content: `❌ Tag "${name}" not found.`, flags: MessageFlags.Ephemeral });
   }
 
-  const ticket = await Ticket.findOne({ discordThreadId: interaction.channel.id }).lean();
+  const ticket = await TTicket.findOne({ discordThreadId: interaction.channel.id }).lean();
   const context = {
     ticket: ticket || {},
     staff: {
@@ -57,10 +62,14 @@ async function handleResponseSend(interaction) {
   };
 
   const content = replaceVariables(tag.content, context);
-  await Tag.updateOne({ name }, { $inc: { useCount: 1 } });
+  await TTag.updateOne({ name }, { $inc: { useCount: 1 } });
   // Tag bodies are staff-authored but may include variable substitutions from user/ticket data.
   // Disable mention parsing so a `@everyone` in a tag body never pings.
   await interaction.reply({ content, allowedMentions: { parse: [] } });
+
+  if (ticket) {
+    record(interaction.user.id, 'response', { ticket, guildId: interaction.guild?.id });
+  }
 }
 
 async function handleResponseCreate(interaction) {
@@ -146,9 +155,8 @@ const RESPONSE_SUBCOMMANDS = {
   list: handleResponseList
 };
 
-/** Autocomplete handler. Currently only /response uses it. */
+/** Autocomplete handler for /response. Routed here by the dispatcher in index.js. */
 async function handleAutocomplete(interaction) {
-  if (interaction.commandName !== 'response') return;
   const subcommand = interaction.options.getSubcommand();
   if (!['send', 'edit', 'delete'].includes(subcommand)) return;
 
@@ -162,4 +170,4 @@ async function handleAutocomplete(interaction) {
   await interaction.respond(filtered);
 }
 
-module.exports = { handleResponse, handleAutocomplete };
+module.exports = { handleResponse, handleAutocomplete, handleResponseSend };