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_deferred/transcript.txt

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+Mira: We need to talk about the weekly dashboard.
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+Jonas: I would prefer moving it to Monday morning.
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+Lea: Monday is rough for support. We usually have backlog cleanup then.
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+Mira: Tuesday might work, but I am not sure.
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+Jonas: Or we keep it on Friday and just make it shorter.
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+Lea: I like shorter, but I need to check with Dana first.
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+Mira: Okay, let's not decide this today.
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+Jonas: Agreed, we need more input.
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+Lea: I will bring Dana's feedback next time.
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+Mira: Thanks, that will help.