Add moderation dashboard, user history & notes (Phase 6a)

Surface the Discord bot's moderation data on the admin panel: a read-only
staff dashboard over the existing mod_actions log, per-user history, staff
notes, and a new moderator role. No bot changes.

Schema
- users.role ENUM gains 'moderator' (CREATE + idempotent ALTER for existing DBs)
- new server-owned mod_notes table (staff_only/admin_only visibility)

Server
- model/moderation: read mod_actions via the shared pool (documented read-only
  cross of the bot/server ownership boundary), correlate accounts through
  user_identities (provider='discord'), flag automated actions via
  staff_user_id === bot_config.application_id; pure reshaping helpers isolated
  in moderation.pure.js so they unit-test without opening a DB pool
- model/modNotes: list/add with role-gated admin_only visibility
- admin/moderation.controller + routes under /api/v1/admin/moderation/* gated by
  requireRole('admin','moderator'); admin_only note writes require admin
- allow assigning 'moderator' in the user create/update validators

Client
- /admin/moderation overview (window tiles, type-filterable recent feed, user
  lookup) and /user/:discordId history (tabs + notes with add-note)
- RoleGate; AdminLayout filters nav and confines moderators to their section
- moderator badge + action-type/auto badges

Deferred (see plan): 6b bot event capture (joins/leaves/filter/spam), 6c appeals
(needs public accounts), 6d /internal/mod-reverse bot reversal callback.

Verified: 116 server unit tests, client build, DB-backed model smoke, full
HTTP/RBAC e2e, and a browser click-through of the dashboard.

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

server/src/model/moderation/moderation.pure.js

@@ -0,0 +1,39 @@
+// Pure reshaping/annotation helpers for the moderation dashboard, deliberately
+// free of any DB (or other side-effecting) imports so they can be unit-tested
+// without opening a database pool. moderation.model re-exports these.
+
+function zeroCounts() {
+  return { ban: 0, kick: 0, mute: 0, warn: 0 }
+}
+
+// Tag each action as automated (staff is the bot) and fold the joined
+// user_identities columns into a linked_account object. The string coercion
+// matters — snowflakes can arrive as number or string from different columns.
+function annotate(rows, appId) {
+  return rows.map((r) => {
+    const isAutomated = appId != null && String(r.staff_user_id) === String(appId)
+    return {
+      ...r,
+      is_automated: isAutomated,
+      linked_account: r.target_site_user_id
+        ? { id: r.target_site_user_id, username: r.target_site_username }
+        : null,
+    }
+  })
+}
+
+// Fold the per-type window rows into the { windows: { '24h', '7d', '30d' } }
+// shape the dashboard tiles consume, zero-filling any type with no rows.
+function reshapeWindows(rows) {
+  const windows = { '24h': zeroCounts(), '7d': zeroCounts(), '30d': zeroCounts() }
+  for (const row of rows) {
+    const t = row.action_type
+    if (windows['24h'][t] === undefined) continue
+    windows['24h'][t] = Number(row.d1) || 0
+    windows['7d'][t] = Number(row.d7) || 0
+    windows['30d'][t] = Number(row.d30) || 0
+  }
+  return { windows }
+}
+
+module.exports = { zeroCounts, annotate, reshapeWindows }