feat: auto-assign Discord role to library members

Implemented automatic Discord role assignment for users who are
members of the NHCarrigan server. This happens on every login:

- Check if user is in Discord server (ID: 1354624415861833870)
- Fetch user's current roles via Discord API
- Assign library member role if they don't have it yet
- Graceful error handling without blocking login

Uses Discord Bot API with proper permissions to manage roles.
Similar pattern to badge refresh on login.

Environment variables added:
- DISCORD_BOT_TOKEN: Bot token for Discord API calls
- LIBRARY_ROLE_ID: Role ID to assign (1474616681023279236)

api/src/app/routes/auth/index.ts

@@ -102,6 +102,53 @@ const authRoutes: FastifyPluginAsync = async (app) => {
         request
       );
 
+      // Assign library member role if user is in Discord server but doesn't have it
+      const libraryRoleId = process.env.LIBRARY_ROLE_ID;
+      if (inDiscord && guildId && libraryRoleId) {
+        try {
+          const memberResponse = await fetch(
+            `https://discord.com/api/users/@me/guilds/${guildId}/member`,
+            {
+              headers: {
+                Authorization: `Bearer ${tokenResult.token.access_token}`,
+              },
+            }
+          );
+
+          if (memberResponse.ok) {
+            const memberData = await memberResponse.json() as { roles: string[] };
+            const hasLibraryRole = memberData.roles.includes(libraryRoleId);
+
+            if (!hasLibraryRole) {
+              const botToken = process.env.DISCORD_BOT_TOKEN;
+              if (botToken) {
+                const assignRoleResponse = await fetch(
+                  `https://discord.com/api/v10/guilds/${guildId}/members/${userData.id}/roles/${libraryRoleId}`,
+                  {
+                    method: "PUT",
+                    headers: {
+                      Authorization: `Bot ${botToken}`,
+                      "Content-Type": "application/json",
+                    },
+                  }
+                );
+
+                if (assignRoleResponse.ok || assignRoleResponse.status === 204) {
+                  app.log.info(`Assigned library role to user ${user.username} (${user.id})`);
+                } else {
+                  app.log.error(
+                    `Failed to assign library role to user ${user.username}: ${assignRoleResponse.status}`
+                  );
+                }
+              }
+            }
+          }
+        } catch (error) {
+          // Don't fail the login if role assignment fails
+          app.log.error({ err: error }, "Error assigning library role");
+        }
+      }
+
       // Set signed cookies and redirect to frontend
       reply
         .setCookie("auth-token", accessToken, {