Migrate the ember/reed bespoke mail watcher to the shared promotion path #376

Follow-up from the envelope-verification-on-promotion work (Refs ops-8mhg).

The ember/reed watcher (tps-mail-watcher.mjs) reads new/ and renames-to-cur/ with no
envelope check, so it delivers unverified bodies — the gap the CLI and openclaw-tps-mail
no longer have now that both route through the shared promote().

Either migrate it onto tps mail watch (which will route through promote()) or retire it.
A census found zero unsigned v1 traffic there, so migrating should be low-risk.

Refs ops-8mhg