Bridgy's Micropub endpoint required per-silo access tokens and posted
raw markdown content directly. Switch to Bridgy's webmention publish
endpoint instead: POST source/target to /publish/webmention and let
Bridgy re-fetch the note page, which now carries hidden verification
links for silos not yet syndicated. Removes the now-unused
config/bridgy.php and BRIDGY_MASTODON_TOKEN env var, and caps both
jobs to a single try since retries would send Bridgy a duplicate
publish webmention.
