Add multi-guild Discord OAuth support

- Users can now login via Bacanaks OR Piccadilly Discord server
- Highest role from all servers is used (superadmin > moderator > user)
- Lazy initialization fixes env loading timing issue
- Updated documentation with implementation details and troubleshooting

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

auth.js

@@ -2,7 +2,7 @@ import { Router } from 'express';
 import jwt from 'jsonwebtoken';
 import { db, VALID_ROLES, initDiscordUsers } from '../db/init.js';
 import { authenticateToken, requireRole } from '../middleware/auth.js';
-import { getDiscordAuthUrl, exchangeCode, getDiscordUser, getGuildMember, getUserRole } from '../services/discord.js';
+import { getDiscordAuthUrl, exchangeCode, getDiscordUser, getGuildMember, getGuildMemberships, getUserRole, getUserRoleFromMemberships } from '../services/discord.js';
 
 const router = Router();
 
@@ -38,15 +38,18 @@ router.get('/discord/callback', async (req, res) => {
     // Get Discord user info
     const discordUser = await getDiscordUser(tokenData.access_token);
 
-    // Check if user is in the guild
-    const member = await getGuildMember(discordUser.id);
+    // Check if user is in any of the configured guilds
+    const memberships = await getGuildMemberships(discordUser.id);
 
-    if (!member) {
+    if (!memberships) {
       return res.redirect(`${frontendUrl}/login?error=not_in_guild`);
     }
 
-    // Determine role based on Discord roles
-    const role = getUserRole(member.roles);
+    // Determine role based on Discord roles (highest role from all servers)
+    const role = getUserRoleFromMemberships(memberships);
+
+    // Use first membership for display name
+    const member = memberships[0].member;
 
     // Get display name (nickname or username)
     const displayName = member.nick || discordUser.global_name || discordUser.username;
@@ -126,13 +129,13 @@ router.post('/refresh-role', authenticateToken, async (req, res) => {
   }
 
   try {
-    const member = await getGuildMember(req.user.discordId);
+    const memberships = await getGuildMemberships(req.user.discordId);
 
-    if (!member) {
-      return res.status(403).json({ error: 'No longer in guild' });
+    if (!memberships) {
+      return res.status(403).json({ error: 'No longer in any guild' });
     }
 
-    const newRole = getUserRole(member.roles);
+    const newRole = getUserRoleFromMemberships(memberships);
 
     db.prepare('UPDATE discord_users SET role = ?, updated_at = CURRENT_TIMESTAMP WHERE discord_id = ?')
       .run(newRole, req.user.discordId);