Split the CLI into command modules and add command-focused tests

[lbliii]

Context

src/kida/cli.py has accumulated many commands and helpers in one file. The CLI is public contract surface, so command-specific behavior should be easier to review and test without threading through a 1,300-line module.

Evidence

• src/kida/cli.py is 1,304 lines.
• main() is about 344 lines.
• The file includes check, render, format, components, explain, README scaffolding, report/data parsing, and shared output helpers.
• CLI behavior is part of the public contract per the root and runtime steward docs.

Proposed Scope

• Move command implementations into small modules under src/kida/cli/ or equivalent while preserving the kida.cli:main entrypoint.
• Keep argument parsing and command dispatch straightforward.
• Add/organize command-specific tests for check/render/readme/report paths.

Done When

• kida.cli:main remains stable.
• Command implementations are reviewable by domain.
• Existing CLI tests and public API snapshot pass.