fix(app): sync keyboard pane focus with active panel (#141)

* fix(app): move keyboard focus to target pane on keyboard navigation (#137)

Add a pane focus registry so each panel type can expose its own focus
callback. When keyboard shortcuts navigate between panes, the workspace
screen calls the target panel's registered focus function, moving DOM
focus to the correct input element.

- Agent panels register a callback that focuses the message input
- Terminal panels register a callback that triggers terminal focus
- Panel-internal focus logic stays inside each panel type
- No DOM selectors or panel knowledge in shared infrastructure

* fix(app): simplify workspace pane focus handoff

packages/app/src/panels/draft-panel.tsx

@@ -17,8 +17,15 @@ function useDraftPanelDescriptor() {
 }
 
 function DraftPanel() {
-  const { serverId, workspaceId, tabId, target, openFileInWorkspace, retargetCurrentTab } =
-    usePaneContext();
+  const {
+    serverId,
+    workspaceId,
+    tabId,
+    target,
+    isPaneFocused,
+    openFileInWorkspace,
+    retargetCurrentTab,
+  } = usePaneContext();
   invariant(target.kind === "draft", "DraftPanel requires draft target");
 
   return (
@@ -27,6 +34,7 @@ function DraftPanel() {
       workspaceId={workspaceId}
       tabId={tabId}
       draftId={target.draftId}
+      isPaneFocused={isPaneFocused}
       onOpenWorkspaceFile={({ filePath }) => {
         openFileInWorkspace(filePath);
       }}