refactor(adk): modernize run-with-google-adk to ADK v2 package with CLI and FastAPI

[dandye]

Summary

• Modernizes run-with-google-adk/ into a standard PEP 621 Python package (mcp-security-agent / mcp_security_agent) powered by Google ADK v2.x.
• Replaces legacy relative path resolution (../../../...) with dynamic package/repo root resolution.
• Replaces custom schema wrappers (MCPToolSetWithSchemaAccess) with native ADK multi-transport toolsets (build_mcp_toolsets) supporting Stdio subprocesses and remote SSE/HTTP URLs.
• Implements centralized Pydantic Settings (AgentSettings) with validated environment and .env loading.
• Introduces dual serving interfaces:
  • Rich interactive terminal REPL (mcp-security-agent chat).
  • Production FastAPI server (mcp-security-agent serve) with /healthz, /info, and /chat endpoints for Cloud Run.
• Adds comprehensive hermetic pytest test suite covering package init, config, toolsets, callbacks, agent, CLI, and REST endpoints (11/11 tests passing).

Changes Made

• Build & Packaging:
  • run-with-google-adk/pyproject.toml: Standard PEP 621 build configuration with CLI entry point mcp-security-agent.
  • run-with-google-adk/sample.env: Clean environment variables template.
  • run-with-google-adk/Dockerfile: Multi-stage container using uv for fast dependency installation and execution.
• Source Package (src/mcp_security_agent/):
  • __init__.py: Package metadata and __version__ = "0.2.0".
  • __main__.py: Executable module entry point.
  • config.py: Centralized AgentSettings using Pydantic Settings with boolean converters and credential fallbacks.
  • toolsets.py: Native ADK MCP toolset builder for SecOps SIEM, SCC, GTI, and SecOps SOAR.
  • callbacks.py: Request context trimming callbacks.
  • agent.py: create_security_agent factory and SOC system prompt.
  • cli.py: Typer CLI with chat, serve, and info subcommands.
  • server/app.py & server/routes.py: FastAPI server factory and endpoints.
• Testing:
  • tests/test_package_init.py
  • tests/test_config.py
  • tests/test_toolsets.py
  • tests/test_callbacks.py
  • tests/test_agent.py
  • tests/test_cli.py
  • tests/test_server.py

Test Plan

• Ran complete hermetic test suite: 11/11 unit tests passed in run-with-google-adk/tests/.
• Verified CLI help output and info command.
• Verified FastAPI /healthz and /info routes.