Add AI-agent caller workflow (verbatim from gitea/agents)

.gitea/workflows/ai-agent.yml

@@ -0,0 +1,15 @@
+name: ai-agent
+run-name: "ai-agent · #${{ github.event.issue.number }}"   # quotes required: bare # starts a YAML comment
+# Standard caller for the shared AI-agent workflow (gitea/agents). Copy this file VERBATIM into
+# any repo that should get the agents — it is identical in every repo. All logic + scripts live in
+# agents/.gitea/workflows/; scripts are fetched from @main at run time. The `jobs.agent` wrapper is
+# required: a reusable (workflow_call) workflow can only be invoked from a caller job, not top-level.
+on:
+  issue_comment:
+    types: [created]
+  issues:
+    types: [opened]
+jobs:
+  agent:
+    uses: gitea/agents/.gitea/workflows/agent.yml@main
+    secrets: inherit