chore: extend testsupport temp-dir fixture and repoguard to cmd/ (change 0398)

[danielhanold]

↩ Change 0398 — Extend the testsupport temp-dir fixture and repoguard to cmd/ real-process test packages

Extends change 0373's temp-dir fixture guard (TestRealProcessPackagesUseFixtureTempDir) from internal/ to internal/ + cmd/, converts the 12 bare t.TempDir() sites in cmd/docket and cmd/releasepkg to testsupport.TempDir(t), and deletes the private gateTempDir helper in cmd/docket/gate_cli_test.go.

• A new cmd/docket population floor keeps a broken cmd/ walk from passing vacuously.
• The guard was mutation-tested: reverting a site reddens it, naming that file, and dropping cmd from the roots reddens the floor.
• Only test code changed.

Results: docs/results/2026-09-27-extend-the-testsupport-temp-dir-fixture-and-repoguard-to-cmd-results.md

Review

Rung: docket-review-standard. Both tasks were built at the standard profile, and the diff is under 1500 lines. Outcome: clean, no findings.

command: go run ./cmd/docket development test
result: green
head_sha: 9c2acb4
ran_at: 2026-09-27T11:37:58Z

The evidence head is the results-commit head that the full suite ran on.