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/de_DE.ini

@@ -2042,3 +2042,8 @@ 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=Max. Breite 0 = Originalaufloesung; DIFF/RGB565 fuer LAN, H264 fuer WAN
 恢复默认=Standard
 质量等级已保存，下次打开远程桌面时生效。=Qualitaetsstufen gespeichert. Wirksam beim naechsten Oeffnen des Remote Desktops.
+屏幕预览质量等级(&P)=Vorschau &Qualitaetsstufen
+屏幕预览质量等级=Vorschau Qualitaetsstufen
+JPEG质量=JPEG Qualitaet
+最大宽度为期望编码宽度；JPEG 质量 1~100=Max. Breite ist die Ziel-Codierbreite; JPEG Qualitaet 1~100
+预览质量等级已保存，下次发送预览时生效。=Vorschau-Qualitaetsstufen gespeichert. Wirksam bei der naechsten Vorschau.