Fix UI review issues: accessibility, i18n, duplicate IDs, URL overflow

- Rename duplicate id="settings-error" to "device-settings-error"
- Add missing i18n key value_source.scene_sensitivity.hint (en/ru/zh)
- Add accessible label to password-toggle and Stop All buttons
- Add aria-hidden toggle on connection overlay
- Fix static image URL overflow with ellipsis truncation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/locales/zh.json

@@ -25,6 +25,7 @@
   "auth.logout.success": "已成功退出",
   "auth.please_login": "请先登录",
   "auth.session_expired": "会话已过期或 API 密钥无效，请重新登录。",
+  "auth.toggle_password": "切换密码可见性",
   "displays.title": "可用显示器",
   "displays.layout": "显示器",
   "displays.information": "显示器信息",
@@ -1162,6 +1163,7 @@
   "value_source.auto_gain.enable": "启用自动增益",
   "value_source.sensitivity": "灵敏度：",
   "value_source.sensitivity.hint": "音频信号的增益倍数（越高反应越灵敏）",
+  "value_source.scene_sensitivity.hint": "亮度信号的增益倍数（越高对亮度变化越敏感）",
   "value_source.smoothing": "平滑：",
   "value_source.smoothing.hint": "时间平滑（0 = 即时响应，1 = 非常平滑/缓慢）",
   "value_source.audio_min_value": "最小值：",
@@ -1309,6 +1311,7 @@
   "target.error.stop_failed": "停止目标失败",
   "target.error.clone_failed": "克隆目标失败",
   "target.error.delete_failed": "删除目标失败",
+  "targets.stop_all.button": "全部停止",
   "targets.stop_all.none_running": "当前没有运行中的目标",
   "targets.stop_all.stopped": "已停止 {count} 个目标",
   "targets.stop_all.error": "停止目标失败",