Add developer LAN mode detection and warning banner

Parse the MQTT "fun" field bit 0x20000000 to detect whether connected
printers have Developer LAN Mode enabled. Show a persistent orange
warning banner when any printer lacks it, since newer firmware silently
rejects MQTT write commands without developer mode.

- Parse fun field into developer_mode on PrinterState
- Add /printers/developer-mode-warnings lightweight polling endpoint
- Include developer_mode in printer status API and support bundle
- Orange banner with affected printer names and wiki link
- Translations for all 6 locales (en, de, fr, it, ja, pt-BR)
- 7 backend + 4 frontend tests

frontend/src/components/Layout.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect, useCallback, useRef, useMemo } from 'react';
 import { NavLink, Outlet, useNavigate, useLocation } from 'react-router-dom';
-import { Printer, Archive, Calendar, BarChart3, Cloud, Settings, Sun, Moon, ChevronLeft, ChevronRight, Keyboard, Github, GripVertical, ArrowUpCircle, Wrench, FolderKanban, FolderOpen, X, Menu, Info, Plug, Bug, LogOut, Key, Loader2, Disc3, type LucideIcon } from 'lucide-react';
+import { Printer, Archive, Calendar, BarChart3, Cloud, Settings, Sun, Moon, ChevronLeft, ChevronRight, Keyboard, Github, GripVertical, ArrowUpCircle, Wrench, FolderKanban, FolderOpen, X, Menu, Info, Plug, Bug, LogOut, Key, Loader2, Disc3, ShieldAlert, type LucideIcon } from 'lucide-react';
 import { useTranslation } from 'react-i18next';
 import { useTheme } from '../contexts/ThemeContext';
 import { KeyboardShortcutsModal } from './KeyboardShortcutsModal';
@@ -149,6 +149,15 @@ export function Layout() {
     refetchInterval: 60 * 1000, // Refresh every minute
   });
 
+  // Check developer LAN mode warnings
+  const { data: devModeWarnings } = useQuery({
+    queryKey: ['developer-mode-warnings'],
+    queryFn: api.getDeveloperModeWarnings,
+    staleTime: 10 * 1000,
+    refetchInterval: 30 * 1000,
+    refetchOnWindowFocus: true,
+  });
+
   // Fetch pending queue items count for badge
   const { data: queueItems } = useQuery({
     queryKey: ['queue', 'pending'],
@@ -807,6 +816,24 @@ export function Layout() {
             </div>
           </div>
         )}
+        {devModeWarnings && devModeWarnings.length > 0 && (
+          <div className="bg-orange-500/20 border-b border-orange-500/30 px-4 py-2 flex items-center justify-between">
+            <div className="flex items-center gap-2 text-sm">
+              <ShieldAlert className="w-4 h-4 text-orange-500" />
+              <span className="text-orange-200">
+                {t('printers.developerModeWarning', {
+                  names: devModeWarnings.map(w => w.name).join(', '),
+                  defaultValue: `Developer LAN mode is not enabled on: ${devModeWarnings.map(w => w.name).join(', ')}. Some features may not work.`
+                })}
+              </span>
+              <a href="https://wiki.bambulab.com/en/knowledge-sharing/enable-developer-mode"
+                 target="_blank" rel="noopener noreferrer"
+                 className="text-orange-400 hover:text-orange-300 font-medium underline ml-2">
+                {t('printers.howToEnable', { defaultValue: 'How to enable' })}
+              </a>
+            </div>
+          </div>
+        )}
         {/* Persistent update banner */}
         {showUpdateBanner && (
           <div className="bg-bambu-green/20 border-b border-bambu-green/30 px-4 py-2 flex items-center justify-between">