feat(mcp): report conservative runtime capabilities

[insane66613]

Summary

Extend server_info with conservative capability information derived from the built-in MCP tool registry and current visibility configuration.

The response adds:

• mcp_capabilities: registered and visible built-in tool counts, group availability, hidden tools, missing tools, and ungrouped tools
• provider_capabilities: an explicit not_probed result

Motivation

MCP clients need a stable way to determine which built-in operations this process can expose, particularly when tool groups are disabled. They should not infer provider/account capabilities from subscription labels or from the existence of unrelated tools.

Safety and compatibility

• all existing server_info fields are retained
• capability reporting is read-only
• group availability is true only when every configured tool in the group is registered and visible
• provider-side features, quotas, plans, and secure-computer access are explicitly not inferred
• optional external/plugin tools are not claimed as built-in capabilities
• no new dependencies

Validation

• uv run ruff check .
• uv run ruff format --check .
• focused capability suite — 4 passed
• manual server_info smoke: 43 registered, 43 visible, no ungrouped built-ins, provider status not_probed
• full upstream-first integration stack on Windows — 1,318 passed, 39 skipped