Fix param validation errors and add TNS config section

- terceros/transaccion: return clear error when required params (doc_num, num_factura) are missing instead of passing empty dict to Firebird causing Column unknown error
- transaccion: remove prefijo from 'por factura' query; parse num_factura as int when digit
- automation: add /preview endpoint to show patient/reception counts before sending; update UI with preview step and disabled run button until preview loads
- config: add TNS credentials section (tns_empresa, tns_usuario, tns_password, api_sucursal) with test-connection button
- config: add POST /config/test-tns endpoint

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

app/routes/transaccion.py

@@ -53,12 +53,13 @@ async def preview_transaccion(
     if not ok:
         return JSONResponse({"success": False, "message": f"Error Firebird: {msg}"})
 
+    if ":num_factura" in q["query_text"] and not factura:
+        fb.disconnect()
+        return JSONResponse({"success": False, "message": "Ingresa el número de factura"})
+
     params = {"fecha_ini": fecha_inicio, "fecha_fin": fecha_fin}
-    if ":num_factura" in q["query_text"] and factura:
-        params["num_factura"] = factura
-        prefijo = configs.get("api_prefijo", "")
-        if prefijo:
-            params["prefijo"] = prefijo
+    if ":num_factura" in q["query_text"]:
+        params["num_factura"] = int(factura) if factura.isdigit() else factura
 
     success, error, rows = fb.execute_query(q["query_text"], params)
     fb.disconnect()
@@ -101,12 +102,13 @@ async def send_transaccion(
     if not ok:
         return JSONResponse({"success": False, "message": f"Error Firebird: {msg}"})
 
+    if ":num_factura" in q["query_text"] and not factura:
+        fb.disconnect()
+        return JSONResponse({"success": False, "message": "Ingresa el número de factura"})
+
     params = {"fecha_ini": fecha_inicio, "fecha_fin": fecha_fin}
-    if ":num_factura" in q["query_text"] and factura:
-        params["num_factura"] = factura
-        prefijo = configs.get("api_prefijo", "")
-        if prefijo:
-            params["prefijo"] = prefijo
+    if ":num_factura" in q["query_text"]:
+        params["num_factura"] = int(factura) if factura.isdigit() else factura
 
     success, error, rows = fb.execute_query(q["query_text"], params)
     fb.disconnect()