feat(vscode): show loading spinner when closing a worktree in agent manager (#487)

* feat(vscode): show loading spinner when closing a worktree in agent manager

Replace the close button with a small spinner while the worktree is being
removed from disk, so the UI feels responsive during the async operation.

* Update README with Kilo Code content and demo gif

* Update README.md

Co-authored-by: kiloconnect[bot] <240665456+kiloconnect[bot]@users.noreply.github.com>

* fix: add .vscode-test/ to kilo-vscode gitignore

The @vscode/test-cli downloads VS Code Electron binaries into
.vscode-test/ when running extension tests. This directory was not
gitignored, causing 1000+ test artifacts to appear in diffs.

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Co-authored-by: Mark IJbema <mark@kilocode.ai>
Co-authored-by: kiloconnect[bot] <240665456+kiloconnect[bot]@users.noreply.github.com>