refactor: extract VS Code extension to packages/agent-os-vscode/ (#491)

Move the VS Code extension from packages/agent-os/extensions/vscode/
to packages/agent-os-vscode/ as a standalone sibling package.

Motivation:
- VS Code TS code was nested inside a Python package (agent-os)
- Security issues in TS code got filed against wrong package
- Python security tools (bandit, ruff) cannot scan TypeScript
- No independent versioning or release cycle
- npm dependencies polluted agent-os directory

Changes:
- git mv packages/agent-os/extensions/vscode -> packages/agent-os-vscode
- Updated cross-references in vscode-extension tutorial
- Removed VSIX build artifacts from tracking

Closes #491

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: imran-siddique