Closes #58

What changed

• Added ignitionrl train for registered project environments.
• Supports learner selection, seed, episode count, max steps, run id and checkpoint id.
• Persists traces, metrics and learner checkpoints through SDK learner experiments.
• Added CLI docs plus success and invalid-argument coverage.

Validation

• bun run --cwd packages/cli typecheck
• bun test packages/cli/test/cli.test.ts
• bun run ci