We should flag the agreement error in "all of it seem"

> The governance, the culture, **all of it seem** really cool, but reading https://ziglang.org/learn/why_zig_rust_d_cpp/ I still don't get _why_ I would use it.

I asked Google's AI if that's an agreement error:

Start by locating Harper's grammar rules and the existing agreement checks, then reproduce the sentence “The governance, the culture, all of it seem really cool.” Done means the checker flags “seem” as an agreement error and includes coverage for this example.

Written by the indexing model from the issue text.