[bugfix] Account.last_status_at is a date, not datetime

[untitaker]

Description

Changes API Account's last_status_at to be a date without time component, for full compat with mastodon.

closes #3418

Checklist

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[untitaker]

converting to draft until we know all tests pass. only ran internal/typeutils/, the rest is too resource-intensive on local hardware.

golangci-lint run does not pass for me on main branch, but this PR does not add new errors. the link in CONTRIBUTING for the installation instructions is out of date, and I suspect I installed too new a version that comes with additional lints: golangci-lint has version 1.61.0 built with go1.23.1 from a1d6c560 on 2024-09-09T17:44:42Z

[tsmethurst]

Thanks! ^_^