By Anuja Bharat Mistry Dec 18 (Reuters) - Birkenstock on Thursday forecast fiscal 2026 profit below Wall Street expectations and annual revenue growth lower than the last two ​years as U.S tariffs hurt margins and cautious consumer spending dampen demand for its ‌sandals and clogs. Its shares fell nearly 10% premarket after the German footwear company warned of a 100 basis-point hit ‌to its annual gross margins from U.S. import duties. Birkenstock, known for its higher-priced "Arizona" sandals and "Bos ...