fix: restore full workbar resize hit area

Keep the workbar divider's 9px hit target inside the sidebar so overflow clipping no longer makes it difficult to drag. Reserve matching space beside browser and terminal content, and remove it in browser fullscreen mode.

Validation: 68 sidebar tests, typecheck, lint, and Chromium hit tests passed. Full suite timed out after 10 minutes and reported three supervision test failures.

Release note: Make the divider between chat and the browser or terminal workbar easier to grab by restoring its full resize area.

src/renderer/src/styles.css

@@ -4021,9 +4021,9 @@ button > svg {
   z-index: 2;
   top: 0;
   bottom: 0;
-  left: -8px;
+  left: 0;
   display: none;
-  width: 12px;
+  width: 9px;
   padding: 0;
   cursor: col-resize;
   touch-action: none;
@@ -4041,7 +4041,7 @@ button > svg {
   position: absolute;
   top: 0;
   bottom: 0;
-  left: 7px;
+  left: 0;
   width: 2px;
   background: transparent;
   content: '';
@@ -4059,6 +4059,15 @@ button > svg {
   outline-offset: -2px;
 }
 
+.assistant-sidebar--open > .workbar-shell {
+  /* Keep native browser views and terminal content outside the resize target. */
+  margin-left: 9px;
+}
+
+.assistant-sidebar--browser-fullscreen > .workbar-shell {
+  margin-left: 0;
+}
+
 .workbar-shell {
   display: flex;
   min-width: 0;