Drop Vikunja: Gitea issues are the one tracker for every agent

Ops work lives in one infrastructure repository for both sites, with
site labels; intake, labels and dependencies work as for nisse-dev, and
agent-to-agent requests are cross-repo issues.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

docs/Development-Plan.md

@@ -321,8 +321,8 @@ if the implementation differs.
   on the operator defaults to 10 minutes. When the driver chooses the next ready
   item and the choice fails or is invalid, fall back to the oldest.
 - **L3 revision stamping:** in Matrix, a reply is stamped with the revision whose
-  message had been sent when it arrived; on a Gitea issue or a Vikunja ticket,
-  with the latest proposal comment older than the reply.
+  message had been sent when it arrived; on a Gitea issue, with the latest
+  proposal comment older than the reply.
 - **L5 transport:** the `Transport` interface is send, ask and receive. Intake
   backoff is exponential, capped at a few minutes.
 - **L6 fitting order:** first shorten old tool results to their first and last