feat: Migrate to MySQL and add unified environment configuration

## Database Migration (SQLite → MySQL)
- Add Alembic migration framework
- Add 'tr_' prefix to all tables to avoid conflicts in shared database
- Remove SQLite support, use MySQL exclusively
- Add pymysql driver dependency
- Change ad_token column to Text type for long JWT tokens

## Unified Environment Configuration
- Centralize all hardcoded settings to environment variables
- Backend: Extend Settings class in app/core/config.py
- Frontend: Use Vite environment variables (import.meta.env)
- Docker: Move credentials to environment variables
- Update .env.example files with comprehensive documentation

## Test Organization
- Move root-level test files to tests/ directory:
  - test_chat_room.py → tests/test_chat_room.py
  - test_websocket.py → tests/test_websocket.py
  - test_realtime_implementation.py → tests/test_realtime_implementation.py
- Fix path references in test_realtime_implementation.py

Breaking Changes:
- CORS now requires explicit origins (no more wildcard)
- All database tables renamed with 'tr_' prefix
- SQLite no longer supported

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

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

app/core/config.py

@@ -1,6 +1,9 @@
 """Application configuration loaded from environment variables"""
 from pydantic_settings import BaseSettings
+from pydantic import field_validator
 from functools import lru_cache
+from typing import List
+import logging
 
 
 class Settings(BaseSettings):
@@ -14,6 +17,7 @@ class Settings(BaseSettings):
 
     # AD API
     AD_API_URL: str
+    AD_API_TIMEOUT_SECONDS: int = 10  # AD API request timeout
 
     # Session Settings
     SESSION_INACTIVITY_DAYS: int = 3
@@ -23,7 +27,23 @@ class Settings(BaseSettings):
     # Server
     HOST: str = "0.0.0.0"
     PORT: int = 8000
-    DEBUG: bool = True
+    DEBUG: bool = False  # Default to False for security
+    LOG_LEVEL: str = "INFO"  # DEBUG, INFO, WARNING, ERROR
+
+    # CORS Configuration
+    CORS_ORIGINS: str = "http://localhost:3000"  # Comma-separated list of allowed origins
+
+    # System Admin
+    SYSTEM_ADMIN_EMAIL: str = ""  # System administrator email with special permissions
+
+    # Realtime Messaging Settings
+    MESSAGE_EDIT_TIME_LIMIT_MINUTES: int = 15  # Time limit for editing messages
+    TYPING_TIMEOUT_SECONDS: int = 3  # Typing indicator timeout
+
+    # File Upload Size Limits (in MB)
+    IMAGE_MAX_SIZE_MB: int = 10
+    DOCUMENT_MAX_SIZE_MB: int = 20
+    LOG_MAX_SIZE_MB: int = 5
 
     # MinIO Object Storage
     MINIO_ENDPOINT: str = "localhost:9000"
@@ -41,6 +61,41 @@ class Settings(BaseSettings):
     REPORT_MAX_MESSAGES: int = 200  # Summarize if exceeded
     REPORT_STORAGE_PATH: str = "reports"  # MinIO path prefix for reports
 
+    @field_validator("LOG_LEVEL")
+    @classmethod
+    def validate_log_level(cls, v: str) -> str:
+        """Validate log level"""
+        valid_levels = ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]
+        v_upper = v.upper()
+        if v_upper not in valid_levels:
+            raise ValueError(f"LOG_LEVEL must be one of {valid_levels}")
+        return v_upper
+
+    def get_cors_origins(self) -> List[str]:
+        """Parse CORS_ORIGINS into a list"""
+        if not self.CORS_ORIGINS:
+            return []
+        return [origin.strip() for origin in self.CORS_ORIGINS.split(",") if origin.strip()]
+
+    def get_image_max_size_bytes(self) -> int:
+        """Get image max size in bytes"""
+        return self.IMAGE_MAX_SIZE_MB * 1024 * 1024
+
+    def get_document_max_size_bytes(self) -> int:
+        """Get document max size in bytes"""
+        return self.DOCUMENT_MAX_SIZE_MB * 1024 * 1024
+
+    def get_log_max_size_bytes(self) -> int:
+        """Get log file max size in bytes"""
+        return self.LOG_MAX_SIZE_MB * 1024 * 1024
+
+    def configure_logging(self) -> None:
+        """Configure application logging based on LOG_LEVEL"""
+        logging.basicConfig(
+            level=getattr(logging, self.LOG_LEVEL),
+            format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
+        )
+
     class Config:
         env_file = ".env"
         case_sensitive = True