ci: add ai-agent caller workflow

.gitea/workflows/ai-agent.yml

@@ -0,0 +1,11 @@
+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