feat: Add MCP Server management functionality

- Implemented encryption utility for securely storing sensitive credentials.
- Added MCPServerModal component for managing MCP server configurations.
- Updated AddToolModal to include MCP server management.
- Enhanced localization with new strings for MCP server features.
- Introduced SVG icons for MCP tools in the frontend.
- Created a new settings section for MCP server configurations in the application.

application/security/encryption.py

@@ -0,0 +1,97 @@
+"""
+Simple encryption utility for securely storing sensitive credentials.
+Uses XOR encryption with a key derived from app secret and user ID.
+Note: This is basic obfuscation. For production, consider using cryptography library.
+"""
+
+import base64
+import hashlib
+import os
+import json
+
+
+def _get_encryption_key(user_id: str) -> bytes:
+    """
+    Generate a consistent encryption key for a specific user.
+    Uses app secret + user ID to create a unique key per user.
+    """
+    # Get app secret from environment or use a default (in production, always use env)
+    app_secret = os.environ.get(
+        "APP_SECRET_KEY", "default-docsgpt-secret-key-change-in-production"
+    )
+
+    # Combine app secret with user ID for user-specific encryption
+    combined = f"{app_secret}#{user_id}"
+
+    # Create a 32-byte key
+    key_material = hashlib.sha256(combined.encode()).digest()
+
+    return key_material
+
+
+def _xor_encrypt_decrypt(data: bytes, key: bytes) -> bytes:
+    """Simple XOR encryption/decryption."""
+    result = bytearray()
+    for i, byte in enumerate(data):
+        result.append(byte ^ key[i % len(key)])
+    return bytes(result)
+
+
+def encrypt_credentials(credentials: dict, user_id: str) -> str:
+    """
+    Encrypt credentials dictionary for secure storage.
+
+    Args:
+        credentials: Dictionary containing sensitive data
+        user_id: User ID for creating user-specific encryption key
+
+    Returns:
+        Base64 encoded encrypted string
+    """
+    if not credentials:
+        return ""
+
+    try:
+        key = _get_encryption_key(user_id)
+
+        # Convert dict to JSON string and encrypt
+        json_str = json.dumps(credentials)
+        encrypted_data = _xor_encrypt_decrypt(json_str.encode(), key)
+
+        # Return base64 encoded for storage
+        return base64.b64encode(encrypted_data).decode()
+
+    except Exception as e:
+        # If encryption fails, store empty string (will require re-auth)
+        print(f"Warning: Failed to encrypt credentials: {e}")
+        return ""
+
+
+def decrypt_credentials(encrypted_data: str, user_id: str) -> dict:
+    """
+    Decrypt credentials from storage.
+
+    Args:
+        encrypted_data: Base64 encoded encrypted string
+        user_id: User ID for creating user-specific encryption key
+
+    Returns:
+        Dictionary containing decrypted credentials
+    """
+    if not encrypted_data:
+        return {}
+
+    try:
+        key = _get_encryption_key(user_id)
+
+        # Decode and decrypt
+        encrypted_bytes = base64.b64decode(encrypted_data.encode())
+        decrypted_data = _xor_encrypt_decrypt(encrypted_bytes, key)
+
+        # Parse JSON back to dict
+        return json.loads(decrypted_data.decode())
+
+    except Exception as e:
+        # If decryption fails, return empty dict (will require re-auth)
+        print(f"Warning: Failed to decrypt credentials: {e}")
+        return {}