Refactor CLI command handlers

[chubes4]

Summary

• Advances Move CLI command implementations out of index.ts #374 by moving the runtime, discovery, workspace-policy, and artifacts command handlers out of packages/cli/src/index.ts into focused packages/cli/src/commands/* modules.
• Keeps the CLI router wiring in index.ts while preserving existing command names, option parsing, JSON output, and help behavior for the extracted slice.
• Leaves the larger recipe-run implementation in index.ts for a separate follow-up slice to keep this PR focused.

Tests

• npm run build
• node packages/cli/dist/index.js help
• node packages/cli/dist/index.js commands --json
• node packages/cli/dist/index.js schema recipe --json
• node packages/cli/dist/index.js recipe validate --recipe examples/recipes/simple-plugin.json --json
• node packages/cli/dist/index.js recipe-run --recipe examples/recipes/simple-plugin.json --dry-run --json
• node packages/cli/dist/index.js validate-blueprint --blueprint '{"steps":[]}' --json
• node packages/cli/dist/index.js run --mount ./examples/simple-plugin:/wordpress/wp-content/plugins/simple-plugin --command wordpress.run-php --arg code-file=./examples/simple-plugin/probe.php --artifacts ./artifacts --json
• npm run workspace-policy-smoke
• npm run discovery-command-smoke
• npm run recipe-dry-run-smoke

Caveats

• npm install was required because the fresh worktree did not have node_modules; incidental package-lock.json version churn was reverted.
• recipe-run and recipe validate internals remain in index.ts; this PR intentionally extracts only a coherent non-recipe command slice.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Refactoring the CLI command handlers, running focused verification, and drafting this PR description for Chris to review.