Centralize Larry routing on agent index

[jblanfrey]

Summary

• Make [[Team/agent-index]] the source of truth for the active roster and routing table in AGENTS.md
• Add a small Larry orchestration boundary gate that checks [[Team/agent-index]] before domain work
• Replace one hardcoded user name with {{USER_NAME}}
• Add .gitattributes for stable Markdown LF endings and ignore local Obsidian config

Notes

• Intentionally does not add new specialists or personal vault/session artifacts
• Keeps the change focused on generic scaffold behavior