Capture member/filter/spam events for the dashboard (Phase 6b)

Light up the moderation dashboard's previously-empty widgets by persisting the
event streams the bot only reacted to in-memory before.

Schema (bot-owned)
- member_events: join/leave, with invite_code/inviter_* for best-effort invite
  attribution on joins
- filter_hits: word / foreign-invite filter deletions (matched + action_taken)
- spam_hits: rate_limit / mass_mention / mass_emoji detections

Bot
- new models memberEvents/filterHits/spamHits
- guildMemberAdd records the join with invite attribution; new inviteTracker.js
  keeps an invite-use cache (GuildInvites intent + inviteCreate/inviteDelete) and
  diffs it on join to find which invite was used — best-effort, never blocks
  auto-role
- new guildMemberRemove records leaves
- messageFilter records filter/spam hits alongside the existing warn/mute;
  inviteFilter now returns the offending code; detectSpam identifies which spam
  rule tripped (preserving the rate-limit-first side-effect order)
- mod_actions still logs the resulting warn/mute — the new tables are additive

Server
- summary extended with joins/leaves/invite_joins/filter_hits/spam_hits per window
- new feeds: /api/v1/admin/moderation/{members,filter-hits,spam-hits}

Client
- overview now shows 8 tiles (mod actions + joins/leaves/filter/spam, joins tile
  notes "N via invite") plus an Events panel with Members/Filter/Spam tabs;
  removed the coming-soon note

Verified: 119 server unit tests, client build, 14-check DB-backed smoke, and a
browser click-through of every tile and events tab (incl. invite attribution).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019rao86n5cXpwAyjdBFEshV

bot/src/discord/guildMemberAdd.js

@@ -1,11 +1,37 @@
-// Auto-role on join. Requires the Server Members privileged intent (already
-// enabled in the Discord Developer Portal per the Phase 1 setup notes).
+// Member join handling: record the join event (with best-effort invite
+// attribution, Phase 6b) then apply the configured auto-role. Requires the
+// Server Members privileged intent (already enabled per the Phase 1 setup notes)
+// and, for invite attribution, the GuildInvites intent.
 const guildConfig = require('../model/guildConfig')
+const memberEvents = require('../model/memberEvents')
+const inviteTracker = require('./inviteTracker')
 const createLogger = require('../utils/logger')
 
-const log = createLogger('autorole')
+const log = createLogger('members')
 
 async function handleGuildMemberAdd(member) {
+  // Attribute the invite first (diffs the invite-use cache), then record the join.
+  // Both are best-effort — a failure here must never block the auto-role below.
+  let invite = { code: null, inviterId: null, inviterTag: null }
+  try {
+    invite = await inviteTracker.attribute(member)
+  } catch (err) {
+    log.warn('invite attribution threw', { userId: member.id, message: err.message })
+  }
+  try {
+    await memberEvents.record({
+      guildId: member.guild.id,
+      eventType: 'join',
+      discordUserId: member.id,
+      username: member.user?.tag,
+      inviteCode: invite.code,
+      inviterId: invite.inviterId,
+      inviterTag: invite.inviterTag,
+    })
+  } catch (err) {
+    log.warn('member join record failed', { userId: member.id, message: err.message })
+  }
+
   try {
     const roleId = await guildConfig.getAutoRoleId(member.guild.id)
     if (!roleId) return