Add document/editor zoom controls

- Persist an app-wide zoom percentage (not per book) and apply it only to the
  writing view (.editor-panes) so the sidebar/navigation stay fixed size
- Add a [-] [100%] [+] control to the chapter and Full Book headers, with a
  click-to-reset level button
- Route Ctrl/Cmd+=, Ctrl/Cmd+-, and Ctrl/Cmd+0 to zoom in/out/reset,
  intercepting the browser's native zoom

src/main/index.ts

@@ -143,6 +143,16 @@ function forwardEditShortcuts(win: BrowserWindow) {
     } else if ((key === "z" && input.shift) || (key === "y" && !input.shift)) {
       event.preventDefault();
       win.webContents.send("folio:redo-requested");
+    } else if (key === "=" || key === "+") {
+      // Ctrl/Cmd+= or Ctrl/Cmd++ → zoom in (intercept the browser's native zoom).
+      event.preventDefault();
+      win.webContents.send("folio:zoom-in-requested");
+    } else if (key === "-") {
+      event.preventDefault();
+      win.webContents.send("folio:zoom-out-requested");
+    } else if (key === "0") {
+      event.preventDefault();
+      win.webContents.send("folio:zoom-reset-requested");
     }
   });
 }
@@ -548,6 +558,18 @@ ipcMain.handle("folio:setTheme", (_e, id: unknown) => {
   return { ok: true };
 });
 
+// Editor zoom preference (percentage). Persisted app-wide, not per book, so the
+// writing view stays at the user's chosen size across books and restarts.
+ipcMain.handle("folio:getZoom", () => {
+  const z = getSetting<number>("zoom", 100);
+  return Number.isFinite(z) && z > 0 ? Math.round(z) : 100;
+});
+ipcMain.handle("folio:setZoom", (_e, pct: unknown) => {
+  const z = typeof pct === "number" && Number.isFinite(pct) ? Math.round(pct) : 100;
+  setSetting("zoom", z);
+  return { ok: true };
+});
+
 ipcMain.handle("folio:importAttachment", async () => {
   const bp = requireBook();
   const { canceled, filePaths } = await showOpenDialog({

src/main/preload.ts

@@ -46,6 +46,8 @@ contextBridge.exposeInMainWorld("folio", {
   copyText: (text: string) => ipcRenderer.invoke("folio:copyText", text),
   getClipboardText: () => ipcRenderer.invoke("folio:getClipboardText"),
   toggleFullscreen: () => ipcRenderer.invoke("folio:toggleFullscreen"),
+  getZoom: () => ipcRenderer.invoke("folio:getZoom"),
+  setZoom: (pct: number) => ipcRenderer.invoke("folio:setZoom", pct),
 
   // theme preference
   getTheme: () => ipcRenderer.invoke("folio:getTheme"),
@@ -84,4 +86,10 @@ contextBridge.exposeInMainWorld("folio", {
     ipcRenderer.on("folio:selectAll-requested", () => cb()),
   onSaveRequested: (cb: () => void) =>
     ipcRenderer.on("folio:save-requested", () => cb()),
+  onZoomInRequested: (cb: () => void) =>
+    ipcRenderer.on("folio:zoom-in-requested", () => cb()),
+  onZoomOutRequested: (cb: () => void) =>
+    ipcRenderer.on("folio:zoom-out-requested", () => cb()),
+  onZoomResetRequested: (cb: () => void) =>
+    ipcRenderer.on("folio:zoom-reset-requested", () => cb()),
 });

src/renderer/book.ts

@@ -51,6 +51,8 @@ export type FolioAPI = {
   toggleFullscreen: () => Promise<boolean>;
   getTheme: () => Promise<string>;
   setTheme: (id: string) => Promise<any>;
+  getZoom: () => Promise<number>;
+  setZoom: (pct: number) => Promise<any>;
   onBookOpened: (cb: (data: { path: string; title: string }) => void) => void;
   onBookClosed: (cb: () => void) => void;
   onChaptersChanged: (cb: () => void) => void;
@@ -67,6 +69,9 @@ export type FolioAPI = {
   onRedoRequested: (cb: () => void) => void;
   onSelectAllRequested: (cb: () => void) => void;
   onSaveRequested: (cb: () => void) => void;
+  onZoomInRequested: (cb: () => void) => void;
+  onZoomOutRequested: (cb: () => void) => void;
+  onZoomResetRequested: (cb: () => void) => void;
 };
 
 const $ = (id: string) => document.getElementById(id) as HTMLElement;
@@ -1334,6 +1339,45 @@ export function initBook(api: FolioAPI) {
   });
   api.onSaveRequested(() => void saveAndNotify());
 
+  // ---- editor zoom (writing view only) ----
+  // Zoom scales the document content area (the .editor-panes containers) so the
+  // sidebar/navigation keep their normal size. The chosen level is persisted
+  // app-wide and re-applied on launch.
+  let currentZoom = 100;
+  function applyZoom(pct: number, persist = true) {
+    const clamped = Math.max(50, Math.min(300, Math.round(pct)));
+    currentZoom = clamped;
+    document.querySelectorAll<HTMLElement>(".editor-panes").forEach((el) => {
+      el.style.zoom = String(clamped / 100);
+    });
+    document.querySelectorAll<HTMLElement>(".zoom-level").forEach((el) => {
+      el.textContent = clamped + "%";
+    });
+    if (persist) void api.setZoom(clamped);
+  }
+  document.querySelectorAll<HTMLElement>(".zoom-control").forEach((ctrl) => {
+    ctrl
+      .querySelector('[data-zoom="out"]')
+      ?.addEventListener("click", () => applyZoom(currentZoom - 10));
+    ctrl
+      .querySelector('[data-zoom="in"]')
+      ?.addEventListener("click", () => applyZoom(currentZoom + 10));
+    ctrl
+      .querySelector('[data-zoom="reset"]')
+      ?.addEventListener("click", () => applyZoom(100));
+  });
+  api.onZoomInRequested(() => applyZoom(currentZoom + 10));
+  api.onZoomOutRequested(() => applyZoom(currentZoom - 10));
+  api.onZoomResetRequested(() => applyZoom(100));
+  void (async () => {
+    try {
+      const z = await api.getZoom();
+      if (typeof z === "number" && z > 0) applyZoom(z, false);
+    } catch {
+      /* keep default 100% */
+    }
+  })();
+
   // Ctrl/Cmd+S saves the current chapter (in addition to the menu item).
   window.addEventListener("keydown", (e) => {
     if ((e.ctrlKey || e.metaKey) && e.key.toLowerCase() === "s") {

src/renderer/index.css

@@ -526,6 +526,32 @@ body.dragging-active * {
   border-color: var(--color-on-accent-border);
 }
 
+/* Editor zoom controls (writing view only; sidebar/nav stay fixed size). */
+.zoom-control {
+  display: inline-flex;
+  align-items: center;
+  gap: 2px;
+}
+.zoom-control .icon-btn {
+  font-size: 1rem;
+  line-height: 1;
+}
+.zoom-control .zoom-level {
+  min-width: 50px;
+  border: 1px solid var(--color-border);
+  background: transparent;
+  color: var(--color-text);
+  border-radius: calc(var(--radius) - 4px);
+  font-size: 0.78rem;
+  padding: 2px 4px;
+  cursor: pointer;
+  text-align: center;
+}
+.zoom-control .zoom-level:hover {
+  background: var(--color-on-accent-soft);
+  border-color: var(--color-on-accent-border);
+}
+
 /* Small accent dot shown next to a chapter's title when it has a color. */
 .row-color-dot {
   flex: 0 0 auto;

src/renderer/index.html

@@ -62,6 +62,11 @@
               <span class="word-count" id="wordCount">words: 0</span>
               <button class="icon-button" id="exportBtn" title="Export book (Markdown)">⬇</button>
               <button class="icon-button" id="exportZipBtn" title="Export bundle (ZIP)">📦</button>
+              <div class="zoom-control" role="group" aria-label="Zoom">
+                <button class="icon-btn" type="button" data-zoom="out" title="Zoom out (Ctrl+-)">&#8722;</button>
+                <button class="zoom-level" type="button" data-zoom="reset" title="Reset zoom to 100% (Ctrl+0)">100%</button>
+                <button class="icon-btn" type="button" data-zoom="in" title="Zoom in (Ctrl+=)">&#43;</button>
+              </div>
             </div>
           </header>
           <div class="editor-toolbar" id="editorToolbar">
@@ -230,6 +235,11 @@
                 </div>
               </div>
               <button class="button button-primary" id="copyAllBtn" title="Copy the entire assembled manuscript as Markdown">Copy All</button>
+              <div class="zoom-control" role="group" aria-label="Zoom">
+                <button class="icon-btn" type="button" data-zoom="out" title="Zoom out (Ctrl+-)">&#8722;</button>
+                <button class="zoom-level" type="button" data-zoom="reset" title="Reset zoom to 100% (Ctrl+0)">100%</button>
+                <button class="icon-btn" type="button" data-zoom="in" title="Zoom in (Ctrl+=)">&#43;</button>
+              </div>
               <span class="save-state" id="fullBookStatus"></span>
             </div>
           </header>