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.

commands/register.js

@@ -415,7 +415,38 @@ async function registerCommands() {
       .setDescription('Set your personal email signature (valediction, display name, tagline)')
       .setContexts([InteractionContextType.Guild])
       .setIntegrationTypes([ApplicationIntegrationType.GuildInstall])
-    .setDefaultMemberPermissions(PermissionFlagsBits.ManageMessages)
+      .setDefaultMemberPermissions(PermissionFlagsBits.ManageMessages),
+
+    new SlashCommandBuilder()
+      .setName('stats')
+      .setDescription('View staff metrics for a given time window')
+      .setContexts([InteractionContextType.Guild])
+      .setIntegrationTypes([ApplicationIntegrationType.GuildInstall])
+      .setDefaultMemberPermissions(PermissionFlagsBits.ManageMessages)
+      .addStringOption(opt =>
+        opt
+          .setName('period')
+          .setDescription('Time window (e.g. "30 days", "3 months", "1 year")')
+          .setRequired(false)
+          .setAutocomplete(true)
+      )
+      .addUserOption(opt =>
+        opt
+          .setName('member')
+          .setDescription('Staff member to view stats for (admin only)')
+          .setRequired(false)
+      )
+      .addStringOption(opt =>
+        opt
+          .setName('source')
+          .setDescription('Filter by ticket source')
+          .setRequired(false)
+          .addChoices(
+            { name: 'All', value: 'all' },
+            { name: 'Email', value: 'email' },
+            { name: 'Discord', value: 'discord' }
+          )
+      )
    ];
 
    const contextMenuCommands = [