feat(menu): add Save As to File menu with Ctrl+Shift+S

- Add 'Save As...' item to native File menu, right under Save
- New IPC event folio:save-as-requested routes through preload to renderer
- Wired in index.ts to call saveChapterAs with current chapter ID

src/main/menu.ts

@@ -39,12 +39,18 @@ export function buildMenu(
        { label: "New", accelerator: "CmdOrCtrl+N", click: onRequestNew },
        { label: "Open", accelerator: "CmdOrCtrl+O", click: onRequestOpen },
        { type: "separator" },
-       {
+        {
-         label: "Save",
+          label: "Save",
-         accelerator: "CmdOrCtrl+S",
+          accelerator: "CmdOrCtrl+S",
-         enabled: !!getState().bookPath,
+          enabled: !!getState().bookPath,
-         click: () => getWindow()?.webContents.send("folio:save-requested"),
+          click: () => getWindow()?.webContents.send("folio:save-requested"),
-       },
+        },
+        {
+          label: "Save As…",
+          accelerator: "CmdOrCtrl+Shift+S",
+          enabled: !!getState().bookPath,
+          click: () => getWindow()?.webContents.send("folio:save-as-requested"),
+        },
        { type: "separator" },
       { label: "Open Recent", submenu: recentItems },
       { type: "separator" },

src/main/preload.ts

@@ -102,6 +102,8 @@ contextBridge.exposeInMainWorld("folio", {
     ipcRenderer.on("folio:selectAll-requested", () => cb()),
   onSaveRequested: (cb: () => void) =>
     ipcRenderer.on("folio:save-requested", () => cb()),
+  onSaveAsRequested: (cb: () => void) =>
+    ipcRenderer.on("folio:save-as-requested", () => cb()),
   onZoomInRequested: (cb: () => void) =>
     ipcRenderer.on("folio:zoom-in-requested", () => cb()),
   onZoomOutRequested: (cb: () => void) =>

src/renderer/book/index.ts

@@ -170,6 +170,15 @@ export function initBook(api: FolioAPI) {
     }
   });
   api.onSaveRequested(() => void hooks.saveAndNotify());
+  api.onSaveAsRequested(async () => {
+    if (!state.selectedId) return;
+    const res = await api.saveChapterAs(state.selectedId);
+    if (res && "error" in res) {
+      showToast("Save As failed");
+    } else if (res && "filePath" in res) {
+      showToast(`Saved to ${basename(res.filePath as string)}`);
+    }
+  });
 
   // ---- comments / annotations wiring ----
   // Already wired through the comments feature's internal listeners; the

src/renderer/book/types.ts

@@ -87,6 +87,7 @@ export type FolioAPI = {
   onRedoRequested: (cb: () => void) => void;
   onSelectAllRequested: (cb: () => void) => void;
   onSaveRequested: (cb: () => void) => void;
+  onSaveAsRequested: (cb: () => void) => void;
   onZoomInRequested: (cb: () => void) => void;
   onZoomOutRequested: (cb: () => void) => void;
   onZoomResetRequested: (cb: () => void) => void;