* feat(mail): bot+mailbox=me validation and dynamic --as help tests
Add validateBotMailboxNotMe helper to shortcuts/mail/helpers.go and
wire it as a Validate callback into +message, +messages, +thread and
+triage, so bot identity combined with the default --mailbox me is
rejected early with a clear fixup hint instead of a late opaque API
error.
The --as help text was already dynamic via AddShortcutIdentityFlag;
add TC-10/TC-11 tests in internal/cmdutil/identity_flag_test.go to
pin that behaviour, and TC-1 through TC-9 in
shortcuts/mail/mail_shortcut_validation_test.go to cover the new
Validate callbacks.
+watch is excluded: its AuthTypes is ["user"], so bot is never valid.
sprint: S2
* test(cmdutil): add Hidden and DefValue assertions to identity flag tests
* fix(mail): add bot+mailbox=me validation to +template-create and +template-update
* fix(mail): add bot+mailbox=me validation to +template-update
* fix(mail): gofmt mail_template_create.go
* fix(mail): gofmt mail_template_update.go
* fix(mail): skip bot+mailbox=me check for print-patch-template local path