feat: Add DatabaseManager and LinkPlayer components, implement authentication and linking logic

- Created DatabaseManager component for managing database access via phpMyAdmin.
- Developed LinkPlayer component to link Discord accounts with game characters, including user authentication and error handling.
- Added mock data files for players, organizations, and projects to handle backend unavailability.
- Implemented AuthService for managing user authentication and session checks.
- Created DatabaseService to fetch and manage player, organization, and project data with fallback to mock data.
- Added HTML page for handling authentication unavailability.
- Developed a test script for validating Docker setup and required files.

services/AuthService.ts

@@ -0,0 +1,54 @@
+import { DiscordUser } from '../types';
+
+// Points to the production backend via Traefik
+const API_URL = 'https://vollidioten.ceraticsoft.de';
+
+class AuthService {
+  private user: DiscordUser | null = null;
+  private listeners: ((user: DiscordUser | null) => void)[] = [];
+
+  constructor() {
+    this.checkSession();
+  }
+
+  getUser(): DiscordUser | null {
+    return this.user;
+  }
+
+  // Check if session cookie exists and is valid
+  async checkSession() {
+    try {
+        const res = await fetch(`${API_URL}/auth/me`, { credentials: 'include' });
+        if (res.ok) {
+            const data = await res.json();
+            this.user = data;
+            this.notifyListeners();
+        }
+    } catch (e) {
+        console.log("Auth check failed (Backend might be offline)", e);
+    }
+  }
+
+  // Redirects to Discord OAuth
+  async login(): Promise<void> {
+     window.location.href = `${API_URL}/auth/discord`;
+  }
+
+  logout() {
+     window.location.href = `${API_URL}/auth/logout`;
+  }
+
+  subscribe(listener: (user: DiscordUser | null) => void) {
+    this.listeners.push(listener);
+    listener(this.user);
+    return () => {
+      this.listeners = this.listeners.filter(l => l !== listener);
+    };
+  }
+
+  private notifyListeners() {
+    this.listeners.forEach(l => l(this.user));
+  }
+}
+
+export const authService = new AuthService();