feat: stamp wait=true so MCP skips HTTP job polling

WhatToChange: /Users/marchon/research/recommended-changes/2026-09-20-forgejo-ci-138
  What-to-Change.md

What was actually done:
- GlobalClient POST includes wait:true

What was not done:
- MCP NATS subscriber (HTTP wait is enough for the client)

tests/test_global_client.py

@@ -64,6 +64,7 @@ async def test_global_stamp_posts_hash_sync_and_maps_receipt():
     assert payload["digest"] == SHA256_EMPTY
     assert payload["hashAlg"] == "SHA256"
     assert payload["restamp"] is False
+    assert payload["wait"] is True
     assert headers["Authorization"] == "Bearer secret"
     assert rec.scope == "global"
     assert rec.receipt_id == "job-1"