feat: add freebuff package (Codebuff AI coding agent)

Add freebuff v0.0.85 from npm registry — a pure JS CLI tool for
AI-assisted coding. Pre-fetches all transitive npm dependencies to
work within the Nix sandbox (no network access during build).

README.md

@@ -14,6 +14,7 @@ A custom Nix overlay and flake providing additional packages not found in upstre
 |---------|-------------|----------|
 | `container-use` | Containerized environments for coding agents | AI Coding Agents |
 | `desloppify` | Multi-language codebase health scanner and technical debt tracker for AI agents | AI Coding Agents |
+| `freebuff` | The world's strongest free coding agent | AI Coding Agents |
 | `goose-cli` | CLI for Goose - a local, extensible, open source AI agent that automates engineering tasks | AI Coding Agents |
 | `graphify` | Turn any folder of code, docs, papers, images, or videos into a queryable knowledge graph | AI Coding Agents |
 | `mcp-gateway` | Universal Model Context Protocol gateway that sits between AI client and MCP tools/servers | MCP Servers |
@@ -107,6 +108,7 @@ nix-overlay/
 ├── packages/                    # Package definitions
 │   ├── default/                # Meta-package listing all packages
 │   ├── desloppify/             # Codebase health scanner for AI agents
+│   ├── freebuff/               # Free coding agent (Codebuff)
 │   ├── flake-inputs/           # Utility for caching flake inputs
 │   ├── goose-cli/              # Goose AI agent CLI
 │   ├── graphify/               # Knowledge graph generator for code folders