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/todo_simple/transcript.txt

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+Omar: The beta signup page still points to the old privacy note.
+
+Nina: Yes, I saw that yesterday.
+
+Omar: Can you update the link before the partner demo?
+
+Nina: Yes, I will update the privacy link by Thursday noon.
+
+Omar: Great. Nothing else on that page from my side.
+
+Nina: I will only touch the link, not the layout.
+
+Omar: Fine.
+
+Nina: Then I have what I need.
+
+Omar: We can move on.
+
+Nina: Yes.