Feature: Add configurable screen-preview quality levels menu

Add a "屏幕预览质量等级 (Screen Preview Quality Levels)" item to the
"高级 (Advanced)" menu that opens a dialog to edit the six preset
PreviewProfile levels (target encode width and JPEG quality) used by the
double-click single-preview and loop-snapshot floating windows. The dialog
edits a working copy in a full grid with per-field validation and a
restore-defaults button; on OK it persists the values to the [preview] INI
section.

ChooseScreenPreviewParams now reads from GetPreviewProfileCfg instead of the
hardcoded GetScreenPreviewProfile table, so preview requests sent after a
change use the configured parameters. LoadPreviewProfilesFromCfg loads the
saved levels at startup, falling back to the built-in defaults. Added
en_US/de_DE/zh_TW translations for the new menu and dialog strings.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/lang/zh_TW.ini

@@ -2033,3 +2033,8 @@ Minimal
 最大宽度 0 表示原始分辨率；DIFF/RGB565 适合局域网，H264 适合跨网=最大寬度 0 = 原始解析度；DIFF/RGB565 適合區域網路，H264 適合跨網
 恢复默认=恢復預設
 质量等级已保存，下次打开远程桌面时生效。=品質等級已儲存，下次開啟遠端桌面時生效。
+屏幕预览质量等级(&P)=螢幕預覽品質等級(&P)
+屏幕预览质量等级=螢幕預覽品質等級
+JPEG质量=JPEG品質
+最大宽度为期望编码宽度；JPEG 质量 1~100=最大寬度為期望編碼寬度；JPEG 品質 1~100
+预览质量等级已保存，下次发送预览时生效。=預覽品質等級已儲存，下次傳送預覽時生效。