W ASHINGTON — House Republicans unveiled a spending bill Saturday that would keep federal agencies funded through Sept. 30, pushing ahead with a go-it-alone strategy that seems certain to spark a major confrontation with Democrats over the contours of government spending. The 99-page bill would provide a slight boost to defense programs while trimming nondefense programs below 2024 budget year levels. That approach is likely to be a nonstarter for most Democrats who have long insisted that