gitea: the merging account writes every repository that builds a registered module, read from the indexer's modules (issue 1945)

car-hunter #2 was approved and its commit status refused 403: mesh-tools only read the
repositories of a user. It is now a write collaborator on each repository the indexer's
modules state names (watched over the bus: at the start and on each registration), read
back and said as gitea.repo.writable; the operator's other repositories stay read-only.
gitea_grant_write and gitea_unwritable_repos do and show it by hand; gitea_commit_statuses
answers merge.writes.

modules/gitea/module.json

@@ -40,6 +40,7 @@
   ],
   "emits": [
     "repo.created",
+    "repo.writable",
     "issue.opened",
     "pull.merged",
     "pull.updated",
@@ -567,6 +568,7 @@
     "mesh-build-go.keys",
     "mesh-build-node.keys",
     "mesh-build-image.keys",
-    "mesh-delivery-checker.owed"
+    "mesh-delivery-checker.owed",
+    "mesh-delivery-indexer.modules"
   ]
 }