Merchant Profile & Lemco API Key Management

[NengakDakup]

Description:
Allow merchants to manage their profile and securely store their Lenco API credentials.

Acceptance Criteria:

• Endpoint for merchants to update profile and business info
• Secure storage and retrieval of Lenco API keys (encryption at rest)
• Validation of Lemco credentials (test connection)

Subtasks:

• Profile update endpoint
• Secure storage for API keys
• Lenco API key validation