Add auto-update and display scale features

Integrates electron-updater for automatic app updates, including IPC and renderer APIs for update status and controls. Adds display scale (zoom) setting to settings UI, persists user preference in localStorage, and applies it on startup. Updates OAuth popup allowlist logic and upgrades Electron to v39.2.7.

renderer/settings.js

@@ -11,6 +11,7 @@ const WEATHER_UNIT_KEY = 'nebula-weather-unit'; // 'auto' | 'c' | 'f'
 const HOME_SEARCH_Y_KEY = 'nebula-home-search-y'; // number (vh)
 const HOME_BOOKMARKS_Y_KEY = 'nebula-home-bookmarks-y'; // number (vh)
 const HOME_GLANCE_CORNER_KEY = 'nebula-home-glance-corner'; // 'br'|'bl'|'tr'|'tl'
+const DISPLAY_SCALE_KEY = 'nebula-display-scale'; // number (50-300)
 
 function showStatus(message) {
   if (statusText && statusDiv) {
@@ -167,6 +168,27 @@ window.addEventListener('DOMContentLoaded', () => {
       notify();
     }));
   } catch (e) { console.warn('Home layout control setup failed', e); }
+
+  // Display scale controls
+  try {
+    const scaleSlider = document.getElementById('display-scale-slider');
+    const scaleValue = document.getElementById('display-scale-value');
+    
+    const initScale = Number(localStorage.getItem(DISPLAY_SCALE_KEY) || 100);
+    if (scaleSlider) {
+      scaleSlider.value = String(initScale);
+      if (scaleValue) scaleValue.textContent = initScale + '%';
+    }
+    
+    if (scaleSlider) {
+      scaleSlider.addEventListener('input', () => {
+        const val = Number(scaleSlider.value);
+        if (scaleValue) scaleValue.textContent = val + '%';
+        localStorage.setItem(DISPLAY_SCALE_KEY, String(val));
+        showStatus(`Display scale set to ${val}%`);
+      });
+    }
+  } catch (e) { console.warn('Display scale setup failed', e); }
 });
 
 // Tabs: simple controller