Separate Schoology API wrapper from main app

[AdamEXu]

To make compliant with school's requests

We will need to:

• Create new repo schoology-service
• Use that as a git submodule in this repo as schoology-service/
• Wire up authentication to ensure it works
• Create API routes for listing upcoming assignments
• Add Convex to send updates to frontend asynchronously

Later, we will also need to work on other services that will likely need to be seperated (eg. indexing-service and other things too complex)

I'd like to keep one-backend strictly for basic auth and as a wrapper for the other services, potentially with a student facing API/MCP if that becomes popular