Add Factory Droids target support

[lukeaus]

Summary

Currently, codegraph supports several agents like Claude Code, Cursor, Codex CLI, etc. for automatic MCP config installation. We should add support for the Factory Droids agent (factory) to allow installing the MCP server configuration into ~/.factory/config.json or ./.factory/config.json.

Proposal

• Introduce a new target factory representing Factory Droids.
• Configure it to automatically write the MCP server configuration to the user's home-level or workspace-level Factory Droids configurations.
• Update the registry and CLI installer prompt to list Factory Droids as a target.

[lukeaus]

PR for this issue: #697