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/api/client.ts

@@ -250,6 +250,8 @@ export interface PrinterStatus {
   big_fan2_speed: number | null;     // Chamber/exhaust fan
   heatbreak_fan_speed: number | null; // Hotend heatbreak fan
   firmware_version: string | null;   // Firmware version from MQTT
+  // Developer LAN mode: true = enabled, false = disabled, null = unknown
+  developer_mode: boolean | null;
   // Queue: user has acknowledged plate is cleared for next queued print
   plate_cleared: boolean;
 }
@@ -2292,6 +2294,8 @@ export const api = {
       `/printers/${id}?delete_archives=${deleteArchives}`,
       { method: 'DELETE' }
     ),
+  getDeveloperModeWarnings: () =>
+    request<{ printer_id: number; name: string }[]>('/printers/developer-mode-warnings'),
   getPrinterStatus: (id: number) =>
     request<PrinterStatus>(`/printers/${id}/status`),
   refreshPrinterStatus: (id: number) =>