fix(frontend): shift-select in gesture direction, not grid order

Shift range-select normalized the range with Math.min/Math.max and
always iterated ascending, so the selection's insertion order (which the
Set preserves and which carries through to e.g. pool add order) ignored
the gesture direction. Iterate anchor → target instead via a shared
selectRange helper, so selecting first→last and last→first yield
correspondingly ordered selections.

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

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

@@ -94,15 +94,22 @@
 	// Select via the keyboard: a plain press toggles the focused card and drops the
 	// range anchor there; a Shift press selects everything from the anchor to the
 	// focused card — the same model as Shift+click on the grid.
+	// Select an inclusive index range in gesture direction (anchor → target) so the
+	// selection's insertion order follows how the user swept, not grid order. The
+	// Set preserves insertion order, so this is what later carries through to e.g.
+	// the order files land in a pool.
+	function selectRange(anchorIdx: number, targetIdx: number) {
+		const step = targetIdx >= anchorIdx ? 1 : -1;
+		for (let i = anchorIdx; i !== targetIdx + step; i += step) {
+			if (files[i]?.id) selectionStore.select(files[i].id!);
+		}
+	}
+
 	function selectFocused(range: boolean) {
 		const idx = focusedId ? files.findIndex((f) => f.id === focusedId) : -1;
 		if (idx < 0) return;
 		if (range && lastSelectedIdx !== null) {
-			const from = Math.min(lastSelectedIdx, idx);
+			selectRange(lastSelectedIdx, idx);
-			const to = Math.max(lastSelectedIdx, idx);
-			for (let i = from; i <= to; i++) {
-				if (files[i]?.id) selectionStore.select(files[i].id!);
-			}
 		} else if (files[idx]?.id) {
 			selectionStore.toggle(files[idx].id!);
 		}
@@ -634,12 +641,8 @@
 			return;
 		}
 		if (e.shiftKey && lastSelectedIdx !== null) {
-			// Range-select between lastSelectedIdx and idx (desktop)
+			// Range-select from the anchor toward idx (desktop), in gesture order.
-			const from = Math.min(lastSelectedIdx, idx);
+			selectRange(lastSelectedIdx, idx);
-			const to = Math.max(lastSelectedIdx, idx);
-			for (let i = from; i <= to; i++) {
-				if (files[i]?.id) selectionStore.select(files[i].id!);
-			}
 			lastSelectedIdx = idx;
 		} else {
 			if (file.id) selectionStore.toggle(file.id);