feat(vcs): Use the editor's find bar in the diff viewer (#148)

Find in the diff viewer (⌘F / ⌘R / ⌘G) opens the editor's find bar instead of CodeMirror's search panel: same field, Match Case / Words / Regex, counter, navigation, filter menu and highlights. In the side-by-side viewer the bar sits over the side with the caret, Replace is offered only on editable sides, and the shortcuts come from the keymap. Esc closes the bar even while a match is selected.

Claude-Session: https://claude.ai/code/session_01Dq6jQQn8ZhRfkkyj3PRutA
Co-authored-by: jaw52 <[email protected]>

src/features/vcs/DiffEditor.module.css

@@ -61,6 +61,29 @@
   font-size: var(--fs-tiny);
   line-height: 15px;
 }
+/* The editor's find bar, over the side it searches (side-by-side) or the whole viewer. */
+.findRow {
+  flex: none;
+  display: flex;
+  background: var(--bg-editor-inline, var(--bg-elev));
+  border-bottom: 1px solid var(--border-editor-tabs, var(--border));
+}
+.findRow > div {
+  flex: 1;
+  min-width: 0;
+  border-bottom: none;
+}
+.findRowSplit > div {
+  flex: 0 0 50%;
+  border-right: 1px solid var(--border);
+}
+.findRowRight {
+  justify-content: flex-end;
+}
+.findRowRight > div {
+  border-right: none;
+  border-left: 1px solid var(--border);
+}
 .message {
   flex: 1;
   display: flex;