feat: Add google-secops Gemini CLI extension with skills

[dandye]

This PR introduces a new Gemini CLI Extension for Google SecOps, providing a self-contained set of security skills for the Gemini CLI.

Features

• Self-Contained Skills: Removes external dependencies by inlining runbook logic directly into the skill definitions.
  • Setup: Configuring the remote MCP server.
  • Triage: Alert triage protocol.
  • Investigate: Malware and Lateral Movement investigations.
  • Hunt: Proactive threat hunting procedures.
• Documentation: Detailed guides in docs/google_secops_extension.md.
• Zero-Dependency: No external submodules required.

This PR is targeting the remote_mcp branch to make the diff clear. We can rebase and change target to main after remote_mcp is merged into main.