feat: redesign v2 — inspector layout fix, editor scroll, diff moved to breadcrumb bar

- Fix editor scroll (min-height: 0 + overflow)
- Properties panel extends full height
- Moved Diff button to git-branch icon in breadcrumb bar
- Minor CSS fixes for app layout

src/components/Editor.css

@@ -17,7 +17,8 @@
 /* BlockNote container */
 .editor__blocknote-container {
   flex: 1;
-  overflow: auto;
+  min-height: 0;
+  overflow-y: auto;
   display: flex;
   justify-content: center;
 }