Preserve the CLI through the shared tuning boundary

[sebawebber]

Parent

#43

What to build

Move the pgconfig CLI onto the shared tuning operation while preserving its
established input conveniences and generated configuration. CLI users should
observe no change, but MCP and CLI recommendations should share one calculation
source.

Acceptance criteria

• The CLI obtains recommendations through the shared tuning boundary rather than invoking the legacy calculation pipeline directly.
• Existing resource autodetection and defaults remain unchanged.
• Existing permissive CLI parsing behavior remains compatible, including behavior intentionally stricter in the MCP contract.
• Existing json, alter_system, and conf output formats remain unchanged.
• The CLI continues to return legacy compatibility recommendations, including listen_addresses, even though MCP omits it.
• Regression tests cover representative explicit inputs, autodetected inputs, defaults, and every output format.
• Existing CLI tests and the complete Go test suite remain green.

Blocked by

• Establish the provenance-aware tuning boundary #44