feat: manage custom appearance policy

webui/src/features/admin/SystemSettingsPanel.tsx

@@ -66,7 +66,8 @@ export default function SystemSettingsPanel({ settings, canWrite, canAccessMaint
         maintenance_mode: draft.maintenance_mode,
         navigation: draft.navigation,
         appearance_palette: draft.appearance_palette,
-        appearance_palette_locked: draft.appearance_palette_locked
+        appearance_palette_locked: draft.appearance_palette_locked,
+        appearance_custom_overrides_allowed: draft.appearance_custom_overrides_allowed
       });
       setDraft(saved);
       setSavedDraft(saved);
@@ -120,6 +121,13 @@ export default function SystemSettingsPanel({ settings, canWrite, canAccessMaint
             help={!canWritePolicy ? "i18n:govoplan-admin.appearance_lock_policy_permission" : undefined}
             label="i18n:govoplan-admin.lock_system_palette"
           />
+          <ToggleSwitch
+            checked={draft.appearance_custom_overrides_allowed}
+            onChange={(appearance_custom_overrides_allowed) => setDraft({ ...draft, appearance_custom_overrides_allowed })}
+            disabled={!canWrite || !canWritePolicy || busy}
+            help={!canWritePolicy ? "i18n:govoplan-admin.appearance_policy_permission" : "i18n:govoplan-admin.custom_overrides_policy_help"}
+            label="i18n:govoplan-admin.allow_custom_appearance_overrides"
+          />
           <AppearancePalettePreview palette={draft.appearance_palette} />
           <p className="muted small-note">i18n:govoplan-admin.system_palette_precedence_help</p>
         </Card>
@@ -156,6 +164,7 @@ function systemSettingsDraftKey(item: SystemSettingsItem): string {
     maintenance_mode: item.maintenance_mode,
     navigation: item.navigation,
     appearance_palette: item.appearance_palette,
-    appearance_palette_locked: item.appearance_palette_locked
+    appearance_palette_locked: item.appearance_palette_locked,
+    appearance_custom_overrides_allowed: item.appearance_custom_overrides_allowed
   });
 }

webui/src/features/admin/systemSettingsModel.ts

@@ -41,7 +41,8 @@ export const SYSTEM_SETTINGS_FALLBACK: SystemSettingsItem = {
   settings: {},
   navigation: null,
   appearance_palette: "default",
-  appearance_palette_locked: false
+  appearance_palette_locked: false,
+  appearance_custom_overrides_allowed: false
 };
 
 export function applySystemSettingsSections(