feat: layout url import

feat: backup import (except chords)
feat: legacy layout import
feat: separate layout, chord & setting backup downloads

src/lib/backup/compat/legacy-layout.ts

@@ -0,0 +1,25 @@
+import type {CharaLayoutFile} from "$lib/share/chara-file"
+
+/**
+ * Converts a legacy CSV-based layout to the modern JSON-based format
+ */
+export function csvLayoutToJson(csv: string, device: CharaLayoutFile["device"] = "one"): CharaLayoutFile {
+  const layout: CharaLayoutFile = {
+    charaVersion: 1,
+    type: "layout",
+    device,
+    layout: [[], [], []],
+  }
+
+  for (const layer of csv.split("\n")) {
+    const [layerId, key, action] = layer.substring(1).split(",").map(Number)
+
+    layout.layout[Number(layerId) - 1][Number(key)] = Number(action)
+  }
+
+  return layout
+}
+
+export function isCsvLayout(csv: string): boolean {
+  return /^(A[123],\d+,\d+\n?)+$/.test(csv)
+}