Timeline fixes and export handles (#10522)

* select an export range from timeline

* height tweak

web/src/hooks/use-timeline-utils.ts

@@ -0,0 +1,26 @@
+import { useCallback } from "react";
+
+export const useTimelineUtils = (segmentDuration: number) => {
+  const alignEndDateToTimeline = useCallback(
+    (time: number): number => {
+      const remainder = time % segmentDuration;
+      const adjustment = remainder !== 0 ? segmentDuration - remainder : 0;
+      return time + adjustment;
+    },
+    [segmentDuration],
+  );
+
+  const alignStartDateToTimeline = useCallback(
+    (time: number): number => {
+      const remainder = time % segmentDuration;
+      const adjustment = remainder === 0 ? 0 : -remainder;
+      return time + adjustment;
+    },
+    [segmentDuration],
+  );
+
+  return {
+    alignEndDateToTimeline,
+    alignStartDateToTimeline,
+  };
+};