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/db/schema.sql

@@ -6,7 +6,7 @@ CREATE TABLE IF NOT EXISTS users (
   id            INT AUTO_INCREMENT PRIMARY KEY,
   username      VARCHAR(32)  NOT NULL UNIQUE,
   password_hash VARCHAR(72)  NOT NULL,
-  role          ENUM('admin','editor') NOT NULL DEFAULT 'admin',
+  role          ENUM('admin','editor','moderator') NOT NULL DEFAULT 'admin',
   totp_secret   VARCHAR(64)  NULL,          -- base32 TOTP secret (opt-in 2FA)
   totp_enabled  TINYINT(1)   NOT NULL DEFAULT 0,
   -- Any session token issued before this instant is rejected (see requireAuth).
@@ -368,6 +368,25 @@ CREATE TABLE IF NOT EXISTS invite_log (
   INDEX idx_invite_log_guild (guild_id, created_at)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 
+-- Staff notes on a Discord user, surfaced in the admin moderation dashboard
+-- (Phase 6). Unlike the tables above, this one is SERVER-owned — it is written
+-- and read only by the main site (moderation.controller), never by the bot.
+-- Keyed by discord_user_id (a snowflake, matching mod_actions.target_user_id) so
+-- notes attach to a Discord identity even when it has no linked site account.
+-- Notes are never user-visible; admin_only notes are further restricted to the
+-- admin role (moderators see staff_only only) — enforced in the query layer.
+CREATE TABLE IF NOT EXISTS mod_notes (
+  id              INT AUTO_INCREMENT PRIMARY KEY,
+  discord_user_id VARCHAR(32)  NOT NULL,
+  author_user_id  INT          NULL,
+  author_tag      VARCHAR(120) NULL,
+  body            TEXT         NOT NULL,
+  visibility      ENUM('staff_only','admin_only') NOT NULL DEFAULT 'staff_only',
+  created_at      DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT fk_mod_notes_author FOREIGN KEY (author_user_id) REFERENCES users(id) ON DELETE SET NULL,
+  INDEX idx_mod_notes_user (discord_user_id, created_at)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
 -- Migrations for databases created before the wiki upgrade. Each statement uses
 -- IF NOT EXISTS so re-running on every boot is a harmless no-op. New installs get
 -- these columns from the CREATE TABLE above; existing installs get them here.
@@ -378,6 +397,10 @@ ALTER TABLE users ADD COLUMN IF NOT EXISTS totp_secret VARCHAR(64) NULL;
 ALTER TABLE users ADD COLUMN IF NOT EXISTS totp_enabled TINYINT(1) NOT NULL DEFAULT 0;
 -- Session-revocation cutoff for databases created before token revocation landed.
 ALTER TABLE users ADD COLUMN IF NOT EXISTS tokens_valid_after DATETIME NULL;
+-- Moderation dashboard (Phase 6): add the 'moderator' role to databases created
+-- before it. MODIFY has no IF NOT EXISTS form, but re-declaring the same ENUM is
+-- an idempotent no-op, so it is safe to run on every boot.
+ALTER TABLE users MODIFY COLUMN role ENUM('admin','editor','moderator') NOT NULL DEFAULT 'admin';
 
 ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS excerpt VARCHAR(400) NULL;
 ALTER TABLE wiki_pages ADD COLUMN IF NOT EXISTS category_id INT NULL;