fix: coerce decimals in fuel-logs enhanced repository methods (refs #244)

The enhanced API path on FuelLogsRepository returned raw pg rows
straight to the service layer, so DECIMAL columns (fuel_units,
cost_per_unit, total_cost, gallons, price_per_gallon) arrived as
strings instead of numbers. The service layer compensated with
scattered Number() coercion in toEnhancedResponse and getVehicleStats,
and EfficiencyCalculationService silently leaned on JS string-to-
number coercion in division. Type signatures across the stack
declared number and the runtime delivered string.

Add a private mapEnhancedRow that coerces all DECIMAL columns with
parseFloat while preserving snake_case keys (the convention the
service layer already uses to access these rows). Apply it in every
enhanced read/write path: createEnhanced, findByVehicleIdEnhanced,
findByUserIdEnhanced, findByIdEnhanced, getPreviousLogByOdometer,
getLatestLogForVehicle, updateEnhanced. Drop the now-redundant
Number() wrappers in toEnhancedResponse and getVehicleStats.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/features/fuel-logs/data/fuel-logs.repository.ts

@@ -247,6 +247,20 @@ export class FuelLogsRepository {
     };
   }
 
+  // Coerces DECIMAL columns from node-postgres strings to numbers while
+  // preserving snake_case row keys used by the enhanced API service callers.
+  private mapEnhancedRow(row: any): any {
+    if (!row) return null;
+    return {
+      ...row,
+      fuel_units: row.fuel_units != null ? parseFloat(row.fuel_units) : row.fuel_units,
+      cost_per_unit: row.cost_per_unit != null ? parseFloat(row.cost_per_unit) : row.cost_per_unit,
+      total_cost: row.total_cost != null ? parseFloat(row.total_cost) : row.total_cost,
+      gallons: row.gallons != null ? parseFloat(row.gallons) : row.gallons,
+      price_per_gallon: row.price_per_gallon != null ? parseFloat(row.price_per_gallon) : row.price_per_gallon,
+    };
+  }
+
   // Enhanced API support (new schema)
   async createEnhanced(data: {
     userId: string;
@@ -293,7 +307,7 @@ export class FuelLogsRepository {
       data.notes ?? null
     ];
     const res = await this.pool.query(query, values);
-    return res.rows[0] ?? null;
+    return this.mapEnhancedRow(res.rows[0] ?? null);
   }
 
   async findByVehicleIdEnhanced(vehicleId: string): Promise<any[]> {
@@ -301,7 +315,7 @@ export class FuelLogsRepository {
       `SELECT * FROM fuel_logs WHERE vehicle_id = $1 ORDER BY date_time DESC NULLS LAST, date DESC NULLS LAST, created_at DESC`,
       [vehicleId]
     );
-    return res.rows;
+    return res.rows.map(r => this.mapEnhancedRow(r));
   }
 
   async findByUserIdEnhanced(userId: string): Promise<any[]> {
@@ -309,12 +323,12 @@ export class FuelLogsRepository {
       `SELECT * FROM fuel_logs WHERE user_id = $1 ORDER BY date_time DESC NULLS LAST, date DESC NULLS LAST, created_at DESC`,
       [userId]
     );
-    return res.rows;
+    return res.rows.map(r => this.mapEnhancedRow(r));
   }
 
   async findByIdEnhanced(id: string): Promise<any | null> {
     const res = await this.pool.query(`SELECT * FROM fuel_logs WHERE id = $1`, [id]);
-    return res.rows[0] ?? null;
+    return this.mapEnhancedRow(res.rows[0] ?? null);
   }
 
   async getPreviousLogByOdometer(vehicleId: string, odometerReading: number): Promise<any | null> {
@@ -322,7 +336,7 @@ export class FuelLogsRepository {
       `SELECT * FROM fuel_logs WHERE vehicle_id = $1 AND odometer IS NOT NULL AND odometer < $2 ORDER BY odometer DESC LIMIT 1`,
       [vehicleId, odometerReading]
     );
-    return res.rows[0] ?? null;
+    return this.mapEnhancedRow(res.rows[0] ?? null);
   }
 
   async getLatestLogForVehicle(vehicleId: string): Promise<any | null> {
@@ -330,7 +344,7 @@ export class FuelLogsRepository {
       `SELECT * FROM fuel_logs WHERE vehicle_id = $1 ORDER BY date_time DESC NULLS LAST, date DESC NULLS LAST, created_at DESC LIMIT 1`,
       [vehicleId]
     );
-    return res.rows[0] ?? null;
+    return this.mapEnhancedRow(res.rows[0] ?? null);
   }
 
   async updateEnhanced(id: string, data: {
@@ -416,6 +430,6 @@ export class FuelLogsRepository {
       return null;
     }
 
-    return result.rows[0];
+    return this.mapEnhancedRow(result.rows[0]);
   }
 }

backend/src/features/fuel-logs/domain/fuel-logs.service.ts

@@ -234,8 +234,8 @@ export class FuelLogsService {
       return { logCount: 0, totalFuelUnits: 0, totalCost: 0, averageCostPerUnit: 0, totalDistance: 0, averageEfficiency: 0, unitLabels: labels };
     }
 
-    const totalFuelUnits = rows.reduce((s, r) => s + (Number(r.fuel_units) || 0), 0);
+    const totalFuelUnits = rows.reduce((s, r) => s + (r.fuel_units || 0), 0);
-    const totalCost = rows.reduce((s, r) => s + (Number(r.total_cost) || 0), 0);
+    const totalCost = rows.reduce((s, r) => s + (r.total_cost || 0), 0);
     const averageCostPerUnit = totalFuelUnits > 0 ? totalCost / totalFuelUnits : 0;
 
     const sorted = [...rows].sort((a, b) => (new Date(b.date_time || b.date)).getTime() - (new Date(a.date_time || a.date)).getTime());
@@ -282,9 +282,9 @@ export class FuelLogsService {
       tripDistance: row.trip_distance ?? undefined,
       fuelType: row.fuel_type as FuelType,
       fuelGrade: row.fuel_grade ?? undefined,
-      fuelUnits: Number(row.fuel_units),
+      fuelUnits: row.fuel_units ?? 0,
-      costPerUnit: Number(row.cost_per_unit),
+      costPerUnit: row.cost_per_unit ?? 0,
-      totalCost: Number(row.total_cost),
+      totalCost: row.total_cost ?? 0,
       locationData: row.location_data ?? undefined,
       notes: row.notes ?? undefined,
       efficiency: efficiency,