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

---------

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

packages/desktop/scripts/dev.ps1

@@ -33,5 +33,5 @@ Write-Host @"
     --kill-others `
     --names "metro,electron" `
     --prefix-colors "magenta,cyan" `
-    "cd `"$AppDir`" && npx expo start --port $($env:EXPO_PORT)" `
+    "cd `"$AppDir`" && `$env:PASEO_WEB_PLATFORM = `"electron`"; npx expo start --port $($env:EXPO_PORT)" `
     "npx wait-on tcp:$($env:EXPO_PORT) && npx electron `"$DesktopDir`""