Support recipe file mounts

[chubes4]

Summary

• Add explicit file / directory typing for workspace recipe mounts.
• Preserve mount type through recipe validation, dry-run planning, and runtime mounting so file mounts are no longer rejected as non-directories.
• Cover typed file mounts in the recipe dry-run smoke test.

Verification

• npm run build
• npm run recipe-dry-run-smoke
• git diff --check
• node packages/cli/dist/index.js run --mount ./artifacts/recipe-dry-run-smoke/fixture-mount.json:/tmp/fixture-mount.json:readonly --command wordpress.run-php --arg "code=echo file_exists('/tmp/fixture-mount.json') ? 'mounted' : 'missing';" --artifacts ./artifacts/file-mount-smoke --json

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Diagnosed the Homeboy/WP Codebox file-mount validation failure, drafted the CLI/schema/runtime plumbing change, and ran local verification. Chris remains responsible for review and merge.