Add support for serving static files from DATA_FILES_DIR

Introduce a new environment variable, `DATA_FILES_DIR`, for configuring static file storage. Updated `docker-compose` files to mount the host directory and propagate the variable. Implemented FastAPI `StaticFiles` to serve files from this directory under the `/files` route.

backend/app/core/config.py

@@ -1,3 +1,5 @@
+import os
+
 from pydantic_settings import BaseSettings
 from typing import Optional, List
 
@@ -6,6 +8,7 @@ class Settings(BaseSettings):
     PROJECT_NAME: str = "EventSpace"
     VERSION: str = "1.0.0"
     API_V1_STR: str = "/api/v1"
+    DATA_FILES_DIR: str = os.getenv('DATA_FILES_DIR', 'data/')
 
     # Database configuration
     POSTGRES_USER: str = "postgres"
@@ -14,7 +17,6 @@ class Settings(BaseSettings):
     POSTGRES_PORT: str = "5432"
     POSTGRES_DB: str = "eventspace"
     DATABASE_URL: Optional[str] = None
-    REFRESH_TOKEN_EXPIRE_DAYS: int = 60
     db_pool_size: int = 20  # Default connection pool size
     db_max_overflow: int = 50  # Maximum overflow connections
     db_pool_timeout: int = 30  # Seconds to wait for a connection
@@ -26,6 +28,8 @@ class Settings(BaseSettings):
     sql_echo_timing: bool = False  # Log query execution times
     slow_query_threshold: float = 0.5  # Log queries taking longer than this
 
+    REFRESH_TOKEN_EXPIRE_DAYS: int = 60
+
     @property
     def database_url(self) -> str:
         """