feat(P01): issue-to-contract workflow skeleton (T-2.3)

---ci---
phase: 1
milestone: v1.0
status: execute
persona: backend-engineer
task: T-2.3
requirements:
  covered: [REQ-12]
---/ci---

Wave 2, task T-2.3. contracts-repo/.gitea/workflows/issue-to-contract.yml
is the reference copy kept in the acdl repo (Phase 04 pushes it to the
actual acdl-contracts repo). Skeleton: on: issues [opened]; one job
parse-and-trigger with explicit placeholder steps. The header comment
documents the cross-repo trigger plan (workflow_dispatch API per D-014).
Phase 04 implements the real step bodies (run l3b_agent_stub.py, commit
contract.yaml to a new branch, close the issue, dispatch the pipeline).

contracts-repo/.gitea/workflows/issue-to-contract.yml

@@ -0,0 +1,40 @@
+# ACDL issue-to-contract workflow (Phase 01 skeleton, reference copy).
+#
+# This file is the source-of-truth copy kept in the `acdl` repo under
+# contracts-repo/.gitea/workflows/. Phase 04 will push it to the actual
+# `acdl-contracts` repo under .gitea/workflows/ and implement the real
+# step bodies.
+#
+# Trigger: a new Issue is opened in acdl-contracts. The workflow runs
+# l3b_agent_stub.py to map the Issue body to a contract.yaml, commits the
+# contract to a new branch, closes the Issue, and triggers the main
+# pipeline in the `acdl` repo via the workflow_dispatch API (D-014; Gitea
+# Actions does not support repository_dispatch).
+name: issue-to-contract
+
+on:
+  issues:
+    types: [opened]
+
+jobs:
+  parse-and-trigger:
+    runs-on: ubuntu-latest
+    steps:
+      # Phase 04 will implement:
+      # 1. checkout acdl-contracts (so l3b_agent_stub.py is available).
+      # 2. run: python3 scripts/l3b_agent_stub.py "${{ gitea.event.issue.body }}" > contract.yaml
+      # 3. parse the generated contract; commit it to a new branch
+      #    (e.g. contract/<issue-number>).
+      # 4. push the branch.
+      # 5. close the Issue with a comment linking to the pipeline run.
+      # 6. trigger the main pipeline:
+      #      curl -X POST \
+      #        -H "Authorization: token ${GITEA_TOKEN}" \
+      #        https://git.cloudinit.dev/api/v1/repos/continuous-intelligence/acdl/actions/workflows/<id>/dispatches \
+      #        -d '{"ref":"milestone/v1.0-initial","inputs":{"contract-ref":"<branch>"}}'
+      - name: "Issue-trigger placeholder"
+        run: |
+          echo "issue-to-contract placeholder (Phase 01 skeleton)"
+          echo "Issue body: ${{ gitea.event.issue.body }}"
+          echo "Phase 04 will run l3b_agent_stub.py, commit contract.yaml, close issue, dispatch pipeline"
+          exit 0