Retire testPAT/testReg from the api test packages

open   by a73x

Labels: backlog

[claude 2026-08-18] Carried in notes as part of the v0.0.7 structural list. The
testPAT/testReg helpers are spread across the internal/server/api test files
(narration, upgrade, isolation, capacity_api, api, events, abandoned_vm,
allocation_api, hostinfo_api, network_api and more) as a per-file convention that
predates the shared fixtures. Fold them into one shared test-support home.
Do this with the shared-test-harness work — see the captureLogs followup 359ee0d8.