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_none/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 because backlog cleanup starts then.
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+Mira: Tuesday might work better for support.
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+Jonas: Tuesday is hard for sales, at least this month.
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+Lea: Or we keep Friday and make the dashboard shorter.
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+Mira: I am not convinced shorter solves the timing issue.
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+Jonas: I am not convinced Monday is actually a problem for everyone.
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+Lea: Dana might have a view, but she is not here.
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+Mira: We are circling now.
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+Jonas: Yes, I do not have anything else to add.
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+Lea: Same here.
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+Mira: Okay, let's move to the budget topic.