fix(files-page): use instant scroll-to-file to match hosted

Drop `behavior: "smooth"` from `window.scrollTo` so the scrollend
fires immediately after a click, and revert the manual-selection
suppress from 800ms back to 100ms — the longer window was a
workaround for the smooth-scroll animation that's no longer needed.

Author: dastratakos

packages/web/src/components/files/file-diff-list.tsx

@@ -36,7 +36,7 @@ export const FileDiffList = forwardRef<FileDiffListHandle, FileDiffListProps>(fu
 				const el = document.getElementById(`file-${filePath}`);
 				if (!el) return;
 				const top = el.getBoundingClientRect().top + window.scrollY - STICKY_HEADER_OFFSET;
-				window.scrollTo({ top, behavior: "smooth" });
+				window.scrollTo({ top });
 			},
 		}),
 		[],

packages/web/src/lib/use-active-file-on-scroll.ts

@@ -2,20 +2,14 @@ import { useCallback, useEffect, useRef, useState } from "react";
 import type { PullRequestFile } from "./diff-types";
 
 const HEADER_OFFSET = 96;
-// Generous enough to outlast browser-defined smooth-scroll animations
-// (typically 300–500ms) so the scrollend that fires when the click-driven
-// scroll settles can't override the user's manual selection.
-const MANUAL_SELECTION_SUPPRESS_MS = 800;
 
 export function useActiveFileOnScroll(files: PullRequestFile[]) {
 	const [activeFilePath, setActiveFilePath] = useState<string | undefined>();
 	const suppressUntilRef = useRef(0);
 
 	const setActiveFileManually = useCallback((path: string) => {
 		setActiveFilePath(path);
-		// Suppress the next scrollend so a click-driven smooth scroll doesn't
-		// re-pick a different file when its animation settles.
-		suppressUntilRef.current = Date.now() + MANUAL_SELECTION_SUPPRESS_MS;
+		suppressUntilRef.current = Date.now() + 100;
 	}, []);
 
 	useEffect(() => {