feat(io): save and open .margin projects with cmd-s and cmd-o

src/project.ts

@@ -0,0 +1,20 @@
+import { save, open } from "@tauri-apps/plugin-dialog";
+import { invoke } from "@tauri-apps/api/core";
+import type { Book } from "./model/book";
+
+const FILTERS = [{ name: "margin book", extensions: ["margin"] }];
+
+export async function chooseSavePath(book: Book): Promise<string | null> {
+  return save({ filters: FILTERS, defaultPath: `${book.metadata.title || "Untitled"}.margin` });
+}
+
+export async function writeBook(book: Book, path: string): Promise<void> {
+  await invoke("write_file", { path, contents: JSON.stringify(book, null, 2) });
+}
+
+export async function openBook(): Promise<{ book: Book; path: string } | null> {
+  const selected = await open({ filters: FILTERS, multiple: false, directory: false });
+  if (typeof selected !== "string") return null;
+  const contents = await invoke<string>("read_file", { path: selected });
+  return { book: JSON.parse(contents) as Book, path: selected };
+}