fix(ui): integrate responsive interface scale (#3423)

Keep normal web headers at 48px, send native zoom directly to the focused main or Mini Chat window, and restore walkthrough widths through validated persisted ratios.

Validated 40 context-panel tests, the focus-aware ThemeProvider regression, UI type-check and Electron syntax checks. Runtime smoke and combined workspace validation follow before publication.

packages/electron/main.mjs

@@ -2308,6 +2308,13 @@ const getMenuTargetWindow = () => {
 
 const dispatchMenuAction = (action) => {
   const target = getMenuTargetWindow();
+  // Zoom actions are consumed by the renderer's DOM listener. Sending them
+  // through both the IPC bridge and the DOM event would invoke the handler
+  // multiple times because preload fans the IPC event back into both paths.
+  if (action === 'zoom-in' || action === 'zoom-out' || action === 'zoom-reset') {
+    dispatchDomEventToWindow(target, 'openchamber:zoom', action);
+    return;
+  }
   emitToWindow(target, 'openchamber:menu-action', action);
   dispatchDomEventToWindow(target, 'openchamber:menu-action', action);
 };
@@ -4864,6 +4871,10 @@ const buildMacMenu = () => {
         { role: 'minimize' },
         { role: 'zoom' },
         { type: 'separator' },
+        { label: 'Zoom In', accelerator: 'CmdOrCtrl+=', click: () => dispatchAction('zoom-in') },
+        { label: 'Zoom Out', accelerator: 'CmdOrCtrl+-', click: () => dispatchAction('zoom-out') },
+        { label: 'Reset Zoom', accelerator: 'CmdOrCtrl+0', click: () => dispatchAction('zoom-reset') },
+        { type: 'separator' },
         { role: 'close' },
       ],
     },
@@ -4977,6 +4988,9 @@ const buildAutoHiddenMenu = () => {
       label: 'Window',
       submenu: [
         { role: 'minimize' },
+        { label: 'Zoom In', accelerator: 'Ctrl+=', click: () => dispatchAction('zoom-in') },
+        { label: 'Zoom Out', accelerator: 'Ctrl+-', click: () => dispatchAction('zoom-out') },
+        { label: 'Reset Zoom', accelerator: 'Ctrl+0', click: () => dispatchAction('zoom-reset') },
         { role: 'togglefullscreen' },
         { type: 'separator' },
         { role: 'close' },