Add comprehensive e2e tests for all CLI commands with mocked API
responses. Fix test infrastructure to handle global state (os.Stdout
capture, HOME env var) and broken test parallelism in stdout-capturing
tests.
- Add testutil_test.go with runFreshCommand, setupE2E, mockAPIServer
- Add e2e_full_test.go with ~40 tests covering auth, mail, contacts,
attachments, folders, labels, drafts, help output
- Add newRootCmdBase() for fresh command trees per test
- Remove t.Parallel() from stdout-capturing and HOME-dependent tests
- Fix SessionWithMockSession to use runFreshCommand (stdout capture)
Co-Authored-By: Paperclip <noreply@paperclip.ing>
