fix: handle Firebird Decimal and datetime types in JSON serialization

- PRECIO and VALORTOTAL are Decimal from fdb driver; convert via _safe_num()
- HORAINICIORECEPCION is a datetime object; use _fmt_hora_str() for HH:MM:SS
- _parse_hora() now handles datetime objects directly (no str() roundtrip)
- Same fixes applied to pacientes.py exam builder
- sync-now endpoint catches exceptions and returns traceback as JSON

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

app/routes/envios.py

@@ -33,5 +33,9 @@ async def erp_sync_now(
     ventana_min: int = Query(default=30, ge=1, le=1440),
     user: dict = Depends(get_current_user),
 ):
-    resultado = await sync_recientes(ventana_min=ventana_min)
-    return JSONResponse(resultado)
+    import traceback as tb
+    try:
+        resultado = await sync_recientes(ventana_min=ventana_min)
+        return JSONResponse(resultado)
+    except Exception as e:
+        return JSONResponse({"ok": False, "error": str(e), "traceback": tb.format_exc()}, status_code=200)