Add NixOS module for deploying nixpkgs-search as systemd services:
- Runs separate MCP servers for options (port 8082) and packages (port 8083)
- Shared database configuration (SQLite or PostgreSQL)
- Separate indexing service that runs before servers start
- options.enable and packages.enable flags (both default to true)
- indexFlags option for customizing index command (--no-packages, etc.)
Also update flake.nix:
- Register new module as nixpkgs-search-mcp
- Set as default nixosModule
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
