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/components/message.tsx

@@ -426,6 +426,8 @@ function getUserMessageAttachmentLabel(attachment: AgentAttachment): string {
       return `PR #${attachment.number}`;
     case "github_issue":
       return `Issue #${attachment.number}`;
+    case "text":
+      return attachment.title ?? "Text attachment";
   }
 }