feat: surface explicit adoption proof in gitea_lock_issue response (Closes #477)

When gitea_lock_issue adopts an existing own branch, the live tool
response now carries explicit, citable adoption-proof fields so #473-style
recovery sessions can quote the lock output directly instead of inferring
adoption from separate offline checks.

- issue_lock_adoption.py: add DECISION_LABELS + decision_label()/
  safe_next_action() helpers; extend build_adoption_proof() with
  adoption_decision, adopted, adopted_branch, adopted_branch_head,
  matcher_summary (boundary-safe reason), competing_branch_check, and
  safe_next_action for all outcomes; add build_non_adoption_lock_proof()
  for adoption-free NO_MATCH metadata.
- gitea_mcp_server.py: attach adoption-free adoption_check block to normal
  (non-adopt) lock responses so they cannot be misread as claiming adoption.
- docs/llm-workflow-runbooks.md: document the adoption/adoption_check
  response blocks and instruct recovery reports to cite them directly.
- tests: explicit-field proof for ADOPT/BLOCK_COMPETING/NO_MATCH,
  substring-collision boundary safety (issue-42 vs issue-420), non-adoption
  proof, and MCP-level live-response assertions.

BLOCK_COMPETING lock attempts still fail closed (raise); no raw API
fallback, branch deletion, force-push, or manual lock seeding introduced.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

gitea_mcp_server.py

@@ -1427,6 +1427,14 @@ def gitea_lock_issue(
             f"Adopted existing branch '{branch_name}' and locked issue "
             f"#{issue_number} for recovery (fail-closed check complete)."
         )
+    else:
+        # #477 AC2: normal (no-adoption) lock responses carry explicit,
+        # adoption-free proof metadata so they stay clear and cannot be
+        # misread as claiming a branch was adopted.
+        result["adoption_check"] = issue_lock_adoption.build_non_adoption_lock_proof(
+            issue_number=issue_number,
+            branch_name=branch_name,
+        )
     if agent_artifacts:
         result["warnings"] = [
             "Agent temp artifacts at repo root (delete before implementation): "