feat(ccb): only show the file label in design mode

In code mode the active file is already obvious from the tab bar and
working-files list, so the vertical CCB label is redundant chrome that
just steals vertical space. In design mode the editor collapses and
those affordances aren't visible — that's the only place the label
earns its spot.

Tag the divider preceding the file group with .ccb-file-divider so the
divider + group can be hidden as a pair, and wrap both in a
`body:not(.ccb-editor-collapsed)` rule. No JS toggle needed; the body
class is already flipped by CentralControlBar when design mode changes.

Adds a "should only be visible in design mode" integ test that
checks :visible on both the label and the leading divider through
enter/exit design-mode transitions.

Author: abose

src/index.html

@@ -969,7 +969,7 @@
                 <i class="fa-solid fa-floppy-disk"></i>
             </a>
         </div>
-        <div class="ccb-divider"></div>
+        <div class="ccb-divider ccb-file-divider"></div>
         <div class="ccb-group ccb-group-file">
             <div id="ccbFileLabel" class="ccb-file-label">
                 <span class="ccb-file-dot">•</span>

src/styles/CentralControlBar.less

@@ -181,6 +181,15 @@
 
 }
 
+/* The file label is only useful in design mode — in code mode the active
+   file is already obvious from the tab bar / working-files list, so the
+   vertical label (and its preceding divider) would be redundant chrome
+   that steals vertical space in the CCB. */
+body:not(.ccb-editor-collapsed) #centralControlBar .ccb-file-divider,
+body:not(.ccb-editor-collapsed) #centralControlBar .ccb-group-file {
+    display: none;
+}
+
 /* Editor collapse: actual layout handled in JS via .content width/visibility */
 .ccb-editor-collapsed .content {
     overflow: hidden;

test/spec/CentralControlBar-integ-test.js

@@ -316,6 +316,22 @@ define(function (require, exports, module) {
                 expect($label.find(".ccb-file-dot").length).toBe(1);
             });
 
+            it("should only be visible in design mode (hidden in code mode)", async function () {
+                // The active file is already obvious from the tab bar / working
+                // files list in code mode, so the vertical label (and its
+                // leading divider) are hidden and only surface in design mode.
+                expect(_$("#ccbFileLabel").is(":visible")).toBe(false);
+                expect(_$("#centralControlBar .ccb-file-divider").is(":visible")).toBe(false);
+
+                await enterDesignMode();
+                expect(_$("#ccbFileLabel").is(":visible")).toBe(true);
+                expect(_$("#centralControlBar .ccb-file-divider").is(":visible")).toBe(true);
+
+                await exitDesignMode();
+                expect(_$("#ccbFileLabel").is(":visible")).toBe(false);
+                expect(_$("#centralControlBar .ccb-file-divider").is(":visible")).toBe(false);
+            });
+
             it("should show the active file's name and clear it when no file is open", async function () {
                 await awaitsForDone(
                     SpecRunnerUtils.openProjectFiles(["somelines.html"]),