Reorganize Docker-related files into docker/ directory

Moved Docker infrastructure files to dedicated docker/ folder:
- config/nginx/default.conf → docker/config/nginx/default.conf
- init.sql → docker/init.sql
- start.sh → docker/start.sh (currently unused)

Updated:
- docker-compose.yml: Adjusted volume paths
- README.md: Updated project structure documentation

Benefits:
- Clear separation between infrastructure (docker/) and application (src/)
- Better project organization
- Easier to understand for new developers

Docker Compose and Dockerfile remain in root for convenience.
All services tested and working correctly.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docker/config/nginx/default.conf

@@ -0,0 +1,31 @@
+server {
+    listen 80;
+    server_name localhost;
+    root /var/www/html;
+    index index.php index.html;
+
+    error_log /var/log/nginx/error.log;
+    access_log /var/log/nginx/access.log;
+
+    location / {
+        try_files $uri $uri/ /index.php?$query_string;
+    }
+
+    location ~ \.php$ {
+        try_files $uri =404;
+        fastcgi_split_path_info ^(.+\.php)(/.+)$;
+        fastcgi_pass localhost:9000;
+        fastcgi_index index.php;
+        include fastcgi_params;
+        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
+        fastcgi_param PATH_INFO $fastcgi_path_info;
+    }
+
+    location ~ /\.ht {
+        deny all;
+    }
+
+    location ~ /\.git {
+        deny all;
+    }
+}