Add a machine-readable scenario catalog command

[bsmensah-ctrl]

Problem

The CLI exposes built-in scenarios through argparse choices, but scripts and instructors cannot discover their event/finding expectations without running each scenario separately.

Proposed change

Add a list-scenarios CLI subcommand that writes a JSON catalog to stdout.

Acceptance criteria

• dll-injection-lab list-scenarios exits 0 and emits valid JSON.
• Each catalog entry includes:
  • name;
  • a short defensive description;
  • event_count;
  • expected_finding_count.
• The catalog includes every name in SCENARIOS; adding a future scenario must not require updating a second hard-coded name list.
• Current expectations are covered by tests: classic has 5 events and 1 finding; cooperative has 3 events and 0 findings.
• The command performs only in-memory synthetic analysis and does not read processes, the network, or platform APIs.
• Add the command to the CLI section of README.md.
• uv run --frozen pytest -q and uv run --frozen ruff check . pass.

Useful starting points

• src/crossview_lab/cli.py
• src/crossview_lab/simulator.py
• src/crossview_lab/analyzer.py
• tests/test_cli.py