Add rtk git rev-parse passthrough

Problem

67 invocations of git rev-parse in 30 days, mostly:

• git rev-parse --show-toplevel
• git rev-parse HEAD
• git rev-parse --abbrev-ref HEAD

These are already minimal output (one line), so there's nothing to compress — but they're not currently routed through rtk git, so they don't show up in rtk gain analytics and break the "everything git goes through rtk" mental model.

Proposal

Add rev-parse to the rtk git passthrough list. No filtering needed — just route it so usage is tracked and behavior is consistent with the rest of the git * family.

Low effort, mostly hygiene.