Establish prompt engineering baseline with Gold Standard tests

- introduce Gold Standard evaluation corpus
- document decision taxonomy
- define prompt-engineering methodology
- add regression workflow
- establish Prompt Version 2 baseline
- validate decision_simple, decision_deferred and decision_none

tests/gold/decision_simple/expected.json

@@ -0,0 +1,13 @@
+{
+  "facts": [],
+  "decisions": [
+    {
+      "decision": "The welcome email will be sent after account activation.",
+      "evidence": "So are we agreed that the welcome email moves to after activation? Ben: Agreed. Cara: Yes, let's do that."
+    }
+  ],
+  "todos": [],
+  "questions": [],
+  "positions": [],
+  "technical": []
+}