feat(branding): force color mode (dark or light) site-wide

backend/src/routes/adminSettings.js

@@ -219,9 +219,17 @@ router.put('/branding', adminAuth, requirePermission('settings.edit'), async (re
       logo_display_header,
       logo_display_hero,
       logo_display_mode,
-      hide_powered_by
+      hide_powered_by,
+      force_color_mode
     } = req.body;
 
+    // Normalize force_color_mode: only 'dark' | 'light' | null are valid.
+    const normalizedForceColorMode = force_color_mode === 'dark'
+      ? 'dark'
+      : force_color_mode === 'light'
+        ? 'light'
+        : null;
+
     // Get current watermark settings hash for change detection
     const oldSettingsHash = await watermarkService.getSettingsHash();
 
@@ -243,7 +251,8 @@ router.put('/branding', adminAuth, requirePermission('settings.edit'), async (re
       logo_display_header,
       logo_display_hero,
       logo_display_mode,
-      hide_powered_by
+      hide_powered_by,
+      force_color_mode: normalizedForceColorMode
     };
 
     // Handle favicon deletion if empty string or null is provided

backend/src/routes/publicSettings.js

@@ -65,6 +65,14 @@ router.get('/', async (req, res) => {
       branding_logo_display_hero: settingsObject.branding_logo_display_hero !== false,
       branding_logo_display_mode: settingsObject.branding_logo_display_mode || 'logo_and_text',
       branding_hide_powered_by: settingsObject.branding_hide_powered_by === true,
+      // Force a specific color mode site-wide. When set, the user toggle
+      // is hidden and the value overrides per-theme/system preference.
+      // Allowed values: 'dark' | 'light' | null (null = no force).
+      branding_force_color_mode: settingsObject.branding_force_color_mode === 'dark'
+        ? 'dark'
+        : settingsObject.branding_force_color_mode === 'light'
+          ? 'light'
+          : null,
       theme_config: settingsObject.theme_config || null,
       default_language: settingsObject.general_default_language || 'en',
       enable_analytics: settingsObject.general_enable_analytics !== false,