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/facts_simple/transcript.txt

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+Elena: Quick status on the warehouse migration.
+
+Tom: The old scanner gateway is still running in aisle three.
+
+Elena: Is that the only one left?
+
+Tom: Yes. Aisles one and two moved to the new gateway last week.
+
+Iris: The new gateway is already handling live scans for receiving.
+
+Elena: Good. Let's keep the rollout note factual.
+
+Tom: No decision needed today.
+
+Iris: Fine.
+
+Elena: Anything else on warehouse?
+
+Tom: No, that is all.