test: fix run env profile cleanup fixture

[stainlu]

Summary

• add a dedicated Linux SSH lease test backend for the env-profile cleanup regression
• give the fixture a reachable local SSH readiness port instead of an unroutable TEST-NET host
• isolate HOME in env-helper tests so local lease claims do not affect assertions

Verification

• env GOCACHE=/private/tmp/crabbox-gocache go test ./internal/cli -run 'TestRunCommandCleansEnvProfileWhenProbeFails|TestRunCommandRejectsWindowsEnvHelperBeforeRemoteCommands' -count=1 -timeout 60s -v
• env GOCACHE=/private/tmp/crabbox-gocache go test ./internal/cli
• env GOCACHE=/private/tmp/crabbox-gocache go test ./internal/providers/modal ./internal/providers/tensorlake ./internal/providers/e2b
• git diff --check