feat: CLI commands for stub manifest generation and inspection

[pgierz]

Context

The tutorial/test infrastructure (#253) includes stub_generator.py which creates NetCDF files from YAML manifests. Currently, manifests must be hand-written.

Proposed CLI Commands

pycmor tutorial inspect

Reads real NetCDF files and generates a stub_manifest.yaml:

pycmor tutorial inspect /path/to/real/output/*.nc -o stub_manifest.yaml

pycmor tutorial generate-stubs

Reads a manifest and writes stub NetCDF files:

pycmor tutorial generate-stubs stub_manifest.yaml -o ./stub_data/

Scope

• ~50-80 lines for the inspect command (read dims/coords/attrs, dump YAML)
• CLI wiring via click/typer
• Tests for roundtrip: real files -> manifest -> stub files -> verify structure matches

Depends on

• feat: test infrastructure + tutorial dataset system #253 (test infrastructure + tutorial system)