Add browser pane element picker (#670)

* feat: add browser pane element picker

Port the browser pane from PR #198 and route picked elements through workspace attachments so the context follows every agent composer in a workspace.

Co-authored-by: Jason Kneen <jason.kneen@bouncingfish.com>

* docs: document electron platform overlays

* fix: harden browser pane navigation

* fix: polish browser tab interactions

* fix: route browser pane focus shortcuts

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Co-authored-by: Jason Kneen <jason.kneen@bouncingfish.com>

packages/app/src/screens/workspace/workspace-tab-menu.ts

@@ -81,6 +81,9 @@ function getCloseButtonTestId(tab: WorkspaceTabDescriptor): string {
   if (tab.target.kind === "draft") {
     return `workspace-draft-close-${tab.target.draftId}`;
   }
+  if (tab.target.kind === "browser") {
+    return `workspace-browser-close-${tab.target.browserId}`;
+  }
   if (tab.target.kind === "setup") {
     return `workspace-setup-close-${encodeFilePathForPathSegment(tab.target.workspaceId)}`;
   }