Sync descriptions and issues, run workflows nightly

mirror.js now keeps repo descriptions in step with GitHub. A new
sync-issues workflow copies issues, PR conversations and comments onto
the mirrors with GitHub's numbering. Shared API helpers move to
gitea-mirrors.js. Every workflow now runs once a night, 1.5 hours apart.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

notify.js

@@ -10,6 +10,7 @@ const labels = {
     ['org visibility change', 'orgVisibilityChanged'],
     ['new mirror', 'mirrorsCreated'],
     ['repo visibility change', 'repoVisibilityChanged'],
+    ['description update', 'descriptionsUpdated'],
     ['failure', 'failures']
   ]],
   rename: ['Missing-mirror check', 'rename-facts.json', [
@@ -27,6 +28,15 @@ const labels = {
     ['uploaded asset', 'assetsUploaded'],
     ['unsynced tag', 'unsyncedTags'],
     ['failure', 'failures']
+  ]],
+  issues: ['Issue sync', 'issue-facts.json', [
+    ['mirror', 'mirrorsChecked'],
+    ['GitHub issue', 'issuesFound'],
+    ['created issue', 'created'],
+    ['updated issue', 'updated'],
+    ['created comment', 'commentsCreated'],
+    ['updated comment', 'commentsUpdated'],
+    ['failure', 'failures']
   ]]
 };
 const md = text => String(text).replace(/[\\`*_[\]#]/g, '\\$&');