tests: CRH sections + DP diag bonus + case 74 regression + fusion propagation

- test_extraction: +21 tests (sections diag_sortie/diag_principal/synthese,
  variantes titres, terminaisons, faux positifs mid-sentence, biosynthèse)
- test_dp_selector: +55 tests (flags, candidates, scoring, hardening DIM,
  bonus +4/+2, evidence excerpt, cas 74 D50→I25.1 corrigé)
- test_fusion: +39 tests (propagation dp_selection evidence/reason/verdict,
  source 2e dossier, pas de crash si aucun DP)
- fixtures: case_74_min.json + 3 fixtures DP existantes

Aucun mock utilisé — données synthétiques uniquement.
Le test cas 74 passe : I25.1 gagne sur D50 grâce au bonus diag_sortie +4.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/resources/case_74_min.json

@@ -0,0 +1,38 @@
+{
+  "description": "Cas 74 — D50 Anémie vs I25.1 SCA. Le patch diag_sortie doit faire gagner I25.1.",
+  "dossier": {
+    "document_type": "crh",
+    "sejour": {"sexe": "M", "age": 68, "duree_sejour": 5},
+    "diagnostic_principal": {
+      "texte": "Anémie",
+      "cim10_suggestion": "D50",
+      "cim10_confidence": "medium",
+      "source": "regex"
+    },
+    "diagnostics_associes": [
+      {
+        "texte": "Stent vasculaire",
+        "cim10_suggestion": "Z95.5",
+        "cim10_confidence": "high",
+        "source": "edsnlp"
+      },
+      {
+        "texte": "SCA (Syndrome Coronarien Aigu)",
+        "cim10_suggestion": "I25.1",
+        "cim10_confidence": "high",
+        "source": "llm_das"
+      }
+    ]
+  },
+  "synthese_nuke1": {
+    "motif": "Douleur thoracique",
+    "conclusion": "Anémie ferriprive sur syndrome coronarien aigu traité par angioplastie.",
+    "diag_sortie": "SCA ST+ antérieur traité par angioplastie coronaire — I25.1",
+    "diag_principal": "",
+    "synthese": ""
+  },
+  "expected": {
+    "chosen_code": "I25.1",
+    "verdict": "CONFIRMED"
+  }
+}