feat: add core MCP server, TrainerClient tools, and unit tests

[abhijeet-dhumal]

Implements the full MCP server infrastructure, all TrainerClient-backed tools, Claude Code plugin, dynamic tool modes, benchmark suite, and project documentation per KEP-936.

What's included

• Core MCP server with tool registration and persona-based access control (readonly, data-scientist, ml-engineer, platform-admin)
• Config, resilience (circuit breaker, rate limiter, retry), security, and structured audit logging layers
• 16 TrainerClient MCP tools + 2 health tools: discovery, lifecycle, monitoring, planning, training submission (fine-tune, custom script, container image)
• 5 MCP prompts (fine-tuning, custom training, troubleshooting, resource planning, monitoring) and 4 MCP resources
• Per-tool RBAC policy engine with namespace-scoping, training parameter bounds, and heuristic script safety scanning
• SDK contract tests to keep MCP tool args aligned with SDK method signatures
• Token-efficient dynamic tool modes (--mode progressive, --mode semantic) to reduce LLM context window overhead
• Claude Code plugin (plugin.json, .mcp.json) with 5 workflow skills
• Benchmark suite: token-usage budgets, CPU/memory profiling, latency P50/P95/P99, and visual graphs
• ROADMAP.md with phased delivery plan through GA
• SECURITY.md with trust model and hardening checklist

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from abhijeet-dhumal. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[abhijeet-dhumal]

Hey @andreyvelich @astefanutti @kramaranya @szaher @Electronic-Waste - the 2nd onboarding phase is ready for review now 🏁
Would appreciate a review when you get a chance 🙏