Unify dark UI surfaces and add adjustable topology canvas background.

Lazy-load module routes, restyle remaining light cards/modals/sidebars, and let canvas background be tuned from the display menu.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/i18n/en.ts

@@ -1464,6 +1464,9 @@ const en = {
     fullscreen: "Fullscreen",
     exitFullscreen: "Exit fullscreen",
     display: "Display",
+    canvasBg: "Canvas background",
+    canvasBgColor: "Background color",
+    canvasBgReset: "Reset light blue",
     hideIp: "Hide IP",
     hideVendor: "Hide vendor",
     hidePorts: "Hide ports",

web/src/i18n/zh.ts

@@ -1458,6 +1458,9 @@ const zh = {
     fullscreen: "全屏显示",
     exitFullscreen: "退出全屏",
     display: "显示",
+    canvasBg: "画布背景",
+    canvasBgColor: "背景色",
+    canvasBgReset: "恢复浅蓝",
     hideIp: "隐藏 IP",
     hideVendor: "隐藏厂商",
     hidePorts: "隐藏端口",