[PR 12] CLAUDE.md Generator

Implement command to auto-generate CLAUDE.md from registered cards.

## Command to implement

```bash
opsml generate claude-md --space
```

Sections: Project Context, Data Sources (DataCards), Models (ModelCards), Skills (SkillCards), MCP Servers.

## Files to create/modify

- `crates/opsml_cli/src/actions/manifest.rs` — add generate_claude_md
- Modify `crates/opsml_cli/src/cli/commands.rs` — add Generate command
- Modify `crates/opsml_cli/src/cli/arg.rs` — add GenerateArgs

## Verification

```bash
cargo test -p opsml-cli -- --nocapture
# Register cards in each registry type
# Run: opsml generate claude-md --space
# Verify: generated CLAUDE.md contains expected sections
```

## Depends on

- #360 (PR 11)

## Blocks

- #362 (PR 13)