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.

nginx.conf

@@ -0,0 +1,51 @@
+server {
+    listen 80;
+    server_name localhost;
+
+    root /usr/share/nginx/html;
+    index index.html;
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    location /api/ {
+        # Try to proxy to backend first
+        proxy_pass http://backend:3000;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+
+        # If backend is unavailable, serve mock data
+        error_page 502 503 504 = @fallback;
+    }
+
+    location @fallback {
+        # Serve mock data from frontend
+        rewrite ^/api/(.*)$ /mock/$1 break;
+        try_files $uri /index.html;
+
+        # Add header to indicate mock data is being used
+        add_header X-Mock-Data "true";
+        add_header X-Backend-Status "unavailable";
+    }
+
+    # Handle auth endpoints
+    location /auth/ {
+        proxy_pass http://backend:3000;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+
+        # Auth endpoints should fail if backend is down
+        error_page 502 503 504 = /auth-unavailable.html;
+    }
+
+    # Handle static assets
+    location /assets/ {
+        expires 1y;
+        add_header Cache-Control "public";
+    }
+}