docs: add development prerequisites to README and CONTRIBUTING

List Rust, Bun, just, Docker, and Node.js with install commands
in the README Development section. Add missing Docker prerequisite
to CONTRIBUTING.md.

Author: pRizz

CONTRIBUTING.md

@@ -10,6 +10,7 @@ Thank you for your interest in contributing to opencode-cloud! This document pro
 - **Node.js 20+**
 - **Bun 1.3.9+**
 - **just** (task runner)
+- **Docker** — [Docker Desktop](https://www.docker.com/products/docker-desktop/) or Docker Engine (for building/running the sandbox container)
 
 ### Installation
 

README.md

@@ -578,10 +578,15 @@ Data (PID files, etc.) is stored at:
 
 ## Development
 
-```bash
-# Bun is required for this repo
-bun --version
+### Prerequisites
 
+- **Rust 1.85+** — `curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh`
+- **Bun 1.3.9+** — `curl -fsSL https://bun.sh/install | bash`
+- **just** (task runner) — `cargo install just` or `brew install just`
+- **Docker** — [Docker Desktop](https://www.docker.com/products/docker-desktop/) or Docker Engine
+- **Node.js 20+** — for the Node CLI wrapper
+
+```bash
 # One-time setup (hooks + deps + submodule bootstrap)
 just setup