feat: core entities, infrastructure, and lead repositories

- 25 domain entities mapped from original Datos/ classes
- 4 enums (EstadoLead, TipoPago, TipoDocumento, TipoDescuento)
- DTOs for Lead, Auth flows
- 6 repository interfaces
- VentasDbContext with EF Core + Npgsql
- LeadRepository (command SPs) and LeadQueryRepository (query SPs) with Dapper
- Program.cs with JWT auth, CORS, DI setup
- appsettings.json with connection string
- .gitignore for bin/obj/node_modules
- ROADMAP.md for daily progress tracking

.gitignore

@@ -0,0 +1,31 @@
+# .NET
+bin/
+obj/
+*.user
+*.suo
+*.cache
+*.dll
+*.pdb
+*.exe
+*.runtimeconfig.json
+*.deps.json
+*.staticwebassets.endpoints.json
+.vs/
+
+# Node
+node_modules/
+.next/
+*.tsbuildinfo
+
+# OS
+.DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+.idea/
+*.swp
+
+# Env
+.env
+*.env.local