feat: Independent Certificate Studio Module

[shafeea360]

Implements a standalone certificate studio module:

• Database schema for templates, generated certificates, and school-specific RSA keys.
• Controller and Service logic for bulk generation and digital signature signing.
• React/Inertia UI for the visual Certificate Studio (drag-and-drop fields over templates).
• Public verification page to validate digital signatures using the school's public key.
• Prepares whatsapp field mapping for future integration.

[Emran025]

Closing in favor of the new architecture where the studio UI is built in the Flutter Teacher app, and Laravel handles batch processing in the background.