BERLIN — The collapse of a €100 billion program to build a European next-generation jet fighter has countries scrambling for options. For nearly a decade, the Future Combat Air System was supposed to embody a new vision of European military power: a French, German and Spanish effort — with Belgium as an observer — to build not just a fighter jet, but an entire networked system of jets, drones, sensors and satellites capable of competing with some of the world's most innovative military aircraft.