feat(cli): add completion subcommand and environment diagnostics to doctor

[ujjwalredd]

Summary

Enhances Developer Experience (DX) by adding a shell completion generator (inspect-robots completion bash|zsh) and environment diagnostics output to inspect-robots doctor.

Changes

• Shell Completion Generator: Added inspect-robots completion bash|zsh subcommand to cli.py that generates ready-to-source bash and zsh completion scripts for framework subcommands and options.
• Doctor Environment Diagnostics: Added check_environment_diagnostics() to conformance.py and updated _cmd_doctor in cli.py to output Python executable path, OS platform, framework version, and optional package installation statuses (rerun-sdk, pillow, griffe, torch).
• Tests & Docs: Added unit tests in test_conformance.py and test_registry_cli.py maintaining 100% test coverage gate. Updated CHANGELOG.md.

Checklist

• pre-commit install done; hooks pass
• Tests added/updated
• Coverage stays at 100% (pytest --cov)
• ruff check . and ruff format --check . pass
• mypy passes (strict)
• CHANGELOG.md updated under "Unreleased"
• Public API changes are reflected in inspect_robots.__all__ and the API-snapshot test
• Core stays NumPy-only (new deps are optional extras, lazily imported)

Related

Closes #359