Improve API capabilities

The current Typefully API is very limited compared to the capabilities offered in the app especially in today's landscape of automation, workflows, and AI agents.

In order of priority:

• Publish to all supported platforms (not just X/Twitter)

• Schedule a post via the API

• Add tags when creating or editing a draft

• Retrieve posts based on filters (since a specific date, status: draft/published/scheduled, etc.)