docs: clarify Router runtime argument contracts

[evander-wang]

Summary

• require Router agents to pass the selected Catalog path to start unchanged
• clarify that Workflow paths are relative to Harness Root and must not gain a harness-graph/ prefix
• document the non-empty string-array contract for Step Result evidence
• assert that installed Router assets retain these instructions

Testing

• npm run check:all
• npm run project:check
• npm run doctor
• npm run package:check
• npm run workflow:activate
• all required Workflow validation and image-generation commands