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/technical_simple/README.md

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+# technical_simple
+
+Tests technical extraction with a corrected diagnosis.
+
+The transcript contrasts two possible causes: certificate expiry and runner configuration. The latter is confirmed as the cause.
+
+Typical LLM mistakes:
+
+- Reporting certificate expiry as the problem.
+- Creating a fix decision even though the group explicitly says no fix is decided.
+- Missing the distinction between fact and technical diagnosis.

tests/gold/technical_simple/expected.json

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+{
+  "facts": [
+    {
+      "fact": "The mobile build failed on the staging runner.",
+      "evidence": "Sofia: The mobile build failed again on the staging runner."
+    },
+    {
+      "fact": "The certificate is valid until October.",
+      "evidence": "Nils: The certificate itself is valid until October."
+    }
+  ],
+  "decisions": [],
+  "todos": [],
+  "questions": [
+    {
+      "question": "Is the mobile build failing with the same error as yesterday?",
+      "evidence": "Nils: Same error as yesterday?"
+    }
+  ],
+  "positions": [],
+  "technical": [
+    {
+      "subject": "iOS staging build",
+      "statement": "The iOS job fails during code signing because the runner uses the old keychain path.",
+      "evidence": "The iOS job now fails during code signing. The problem is that the runner uses the old keychain path."
+    },
+    {
+      "subject": "Failure classification",
+      "statement": "The failure is a runner configuration issue, not a certificate expiry issue.",
+      "evidence": "So it is a runner configuration issue, not a certificate expiry issue. Sofia: Exactly."
+    }
+  ]
+}

tests/gold/technical_simple/transcript.txt

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+Sofia: The mobile build failed again on the staging runner.
+
+Nils: Same error as yesterday?
+
+Sofia: No, different. The iOS job now fails during code signing.
+
+Nils: The certificate itself is valid until October.
+
+Sofia: Right. The problem is that the runner uses the old keychain path.
+
+Nils: So it is a runner configuration issue, not a certificate expiry issue.
+
+Sofia: Exactly.
+
+Nils: We are not deciding the fix today.
+
+Sofia: Okay.
+
+Nils: Next item.