fix(frontend): scroll the grid to follow the keyboard focus

Arrowing up/down moved the focus ring but the view didn't follow: the
card was scrolled with scrollIntoView({block:'nearest'}), which aligns to
the scroller's edges and is unaware of the fixed bottom navbar overlaying
the scroll area — so the newly focused row slid under the navbar. Replace
it with a manual scroll that keeps the focused card inside the scroller
with a top margin and a bottom margin sized for the navbar.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/files/+page.svelte

@@ -71,12 +71,29 @@
 		focusedId = files[next]?.id ?? null;
 		if (next >= files.length - gridCols() * 2 && hasMore && !loading) void loadMore();
 		const id = focusedId;
-		requestAnimationFrame(() => {
+		requestAnimationFrame(() => keepFocusedInView(id));
+	}
+
+	// Keep the focused card within the scroller, leaving a margin at the bottom for
+	// the fixed navbar (which overlaps the scroll area and otherwise hides the row
+	// the focus moves onto). scrollIntoView can't account for that overlay.
+	const FOCUS_MARGIN_TOP = 8;
+	const FOCUS_MARGIN_BOTTOM = 72; // ~navbar height + gap
+
+	function keepFocusedInView(id: string | null) {
+		if (!id || !scrollContainer) return;
 		const idx = files.findIndex((f) => f.id === id);
-			scrollContainer
+		const card = scrollContainer.querySelector<HTMLElement>(`[data-file-index="${idx}"]`);
-				?.querySelector<HTMLElement>(`[data-file-index="${idx}"]`)
+		if (!card) return;
-				?.scrollIntoView({ block: 'nearest' });
+		const cardRect = card.getBoundingClientRect();
-		});
+		const scRect = scrollContainer.getBoundingClientRect();
+		const top = cardRect.top - scRect.top;
+		const bottom = cardRect.bottom - scRect.top;
+		if (top < FOCUS_MARGIN_TOP) {
+			scrollContainer.scrollTop += top - FOCUS_MARGIN_TOP;
+		} else if (bottom > scRect.height - FOCUS_MARGIN_BOTTOM) {
+			scrollContainer.scrollTop += bottom - (scRect.height - FOCUS_MARGIN_BOTTOM);
+		}
 	}
 
 	// Action keys operate on the selection; with nothing selected they fall back to