feat: travel calculation (km, CO2, frais réels fiscaux)

app/business/travel_calc.py

@@ -0,0 +1,25 @@
+def compute_km_for_entry(journey_profile_id: str | None, journeys: dict) -> dict[str, int]:
+    if not journey_profile_id:
+        return {}
+    profile = journeys.get(journey_profile_id, {})
+    return dict(profile.get("distances", {}))
+
+
+def compute_co2_grams(km_by_vehicle: dict[str, int], vehicles: dict) -> float:
+    total = 0.0
+    for vehicle_id, km in km_by_vehicle.items():
+        vehicle = vehicles.get(vehicle_id, {})
+        co2 = vehicle.get("co2_per_km", 0)
+        total += km * co2
+    return total
+
+
+def compute_frais_reels(total_km_voiture: float, tranches: list[dict]) -> float:
+    if not tranches or total_km_voiture <= 0:
+        return 0.0
+    for tranche in tranches:
+        km_max = tranche["km_max"]
+        if km_max == 0 or total_km_voiture <= km_max:
+            return total_km_voiture * tranche["taux"] + tranche.get("forfait", 0)
+    last = tranches[-1]
+    return total_km_voiture * last["taux"] + last.get("forfait", 0)