Display course grades and last update time on /grades overview page

[Cfrolich13]

This PR was mostly vibecoded in Antigravity. It "works on my machine," but I still need to test some more edge cases before I mark ready for review. I'm open to feedback.

[vercel]

@Cfrolich13 is attempting to deploy a commit to the 33tm Team on Vercel.

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[Cfrolich13]

I'm not attempting to deploy anything right now. I just opened a draft PR.

[33tm]

Hey! Thanks for the contribution.

I'm aware that preview grades are a highly requested feature; however, there are still some architectural issues that need to be addressed before going forward with a potential merge.

The server makes a baseline of 6 requests (growing with the number of assignments) to the Schoology API per section. Since many users have over 7 sections, calling the same endpoint for all of them would exceed Schoology's 50req/5sec rate limit. At some point, I'd be interested in making a new endpoint that aggregates higher level summaries of all sections, but this would require use of the /multiget endpoint which is quite slow and possibly unsuitable for this use.

As a side note;; I'll make accessing the server locally easier so you don't have to use the workaround in your PR.