Remove the AI-agent workflow caller

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015XiQYLY5JBuwam5nuVnBfz

.gitea/workflows/ai-agent.yml

@@ -1,11 +0,0 @@
-name: ai-agent
-run-name: "ai-agent · #${{ github.event.issue.number }}"
-on:
-  issue_comment:
-    types: [created]
-  issues:
-    types: [opened]
-jobs:
-  agent:
-    uses: gitea/agents/.gitea/workflows/agent.yml@main
-    secrets: inherit