refactor(studio): the settings window loses its enlarge mode and keeps one close button

The sheet already fills the window, so enlarging only took it over the title bar and added three window buttons beside its own two. The control, the stored preference, the window buttons it summoned and the drag-region rules that went with it are removed; the board draws no buttons in that corner besides closing.

tools/repolint/baseline.json

@@ -7,7 +7,7 @@
     "commented-code": 0,
     "complexity": 666,
     "css-important": 127,
-    "css-size": 8878,
+    "css-size": 8876,
     "doc-language": 0,
     "doc-owner": 27,
     "doc-prose": 1434,
@@ -78,7 +78,7 @@
     },
     "desktop/frontend-next/src/styles/app.css": {
       "css-important": 24,
-      "css-size": 5260
+      "css-size": 5258
     },
     "desktop/frontend-next/src/styles/studio.css": {
       "css-important": 103,