[yunze7373]

Summary

Adds support for Meta's Muse Code agent as a first-class MCP client (muse-code), conforming to live-verified schema requirements:

• Uses camelCase mcpServers top-level section with type: "streamable-http" and mode: "optional"
• Defaults to OAuth 2.1 + PKCE authentication flow (muse mcp login XMemo) without leaking credentials to settings.json
• Automatically initializes schema_version: 1 when creating a new settings file while preserving existing settings and versions
• Seamlessly migrates legacy mcp_servers to mcpServers and fails closed on dual-section conflict
• Detects pre-existing lowercase xmemo duplicate entries
• Scopes atomic write via temp-file + rename to muse-code while preserving symlinks via fs.realpath across all JSON clients
• Provides muse mcp login XMemo next steps guidance on xmemo mcp add muse-code --write and xmemo setup muse

Verification

• 144/144 unit tests passing across cli, client-registry, and init suites
• npm run lint clean (0 errors)
• Isolated real-file acceptance and negative tests passing