Switch Bridgy syndication from Micropub to webmention

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.

resources/views/templates/note.blade.php

@@ -1,4 +1,10 @@
 <div class="h-entry">
+    @unless($note->mastodon_url)
+        <a href="https://brid.gy/publish/mastodon" style="display:none"></a>
+    @endunless
+    @unless($note->bluesky_url)
+        <a href="https://brid.gy/publish/bluesky" style="display:none"></a>
+    @endunless
     @if ($note->in_reply_to)
         <div class="u-in-reply-to h-cite reply-to">
             In reply to <a href="{{ $note->in_reply_to }}" class="u-url">{{ $note->in_reply_to }}</a>