Add rustup for on-demand Rust support, document JS/TS development

Install rustup-init binary from Rust CDN. Users bootstrap Rust with
'rustup-init -y' — persists via devbox-rustup and devbox-cargo volumes.
Add JavaScript/TypeScript development docs (Node.js + npm in base, Bun in OMOS).

README.md

@@ -34,6 +34,7 @@ docker compose run --rm devbox
 - **MCP server support** — Node.js included for `npx`-based MCP servers
 - **Non-root user** — runs as `developer` with UID auto-matched to workspace owner (sudo available)
 - **Python via uv** — `uv` package manager included; install Python on demand with `uv python install`
+- **Rust via rustup** — `rustup-init` included; bootstrap Rust on demand with `rustup-init -y`
 - **Optional runtimes** — Python (apt), Go via build args (Node.js always included — required for opencode v1.x)
 - **Multi-agent orchestration** — optional [oh-my-opencode-slim](https://github.com/alvinunreal/oh-my-opencode-slim) integration via build arg
 - **AWS CLI v2** — built-in SSO/Bedrock authentication with headless device-code flow
@@ -172,6 +173,61 @@ volumes:
 
 Project virtual environments (`.venv`) are stored in your workspace directory and persist automatically via the `/workspace` bind mount.
 
+### Rust development with rustup
+
+The image includes `rustup-init`, the Rust toolchain installer. Rust is not pre-installed but can be bootstrapped on demand:
+
+```bash
+# One-time setup: install Rust toolchain (~300MB, persists with volumes)
+rustup-init -y
+source ~/.cargo/env
+
+# Now use Rust normally
+cargo new my-project
+cargo build
+cargo run
+```
+
+To persist Rust toolchains and cargo data across container restarts, add named volumes to your `docker-compose.yml`:
+
+```yaml
+volumes:
+  - devbox-rustup:/home/developer/.rustup
+  - devbox-cargo:/home/developer/.cargo
+
+volumes:
+  devbox-rustup:
+  devbox-cargo:
+```
+
+### JavaScript and TypeScript
+
+The base image includes **Node.js 22** and **npm** — sufficient for most JavaScript and TypeScript development:
+
+```bash
+# Initialize a new project
+npm init -y
+
+# Install dependencies
+npm install
+
+# Run TypeScript (via tsx, ts-node, etc.)
+npx tsx src/index.ts
+
+# Use npx for one-off tools
+npx tsc --init
+```
+
+The OMOS image variant also includes **Bun**, a faster JavaScript runtime and package manager:
+
+```bash
+bun init
+bun install
+bun run src/index.ts
+```
+
+Node modules are stored in your project directory under `/workspace` and persist automatically.
+
 ### Rebuilding the Image
 
 `docker compose run` and `docker compose up` use the existing image — they **do not rebuild** when you change the Dockerfile or build args (e.g. updating `OPENCODE_VERSION`). Rebuild explicitly:
@@ -345,7 +401,7 @@ Container (Debian bookworm)
 ├── opencode binary
 ├── oh-my-opencode-slim (optional — multi-agent orchestration plugin, includes Bun)
 ├── AWS CLI v2 (SSO + Bedrock auth)
-├── neovim 0.12, tmux, htop, bat, eza, zoxide, uv, make
+├── neovim 0.12, tmux, htop, bat, eza, zoxide, uv, rustup, make
 ├── git, ssh, ripgrep, fd, fzf, jq, curl, tree
 ├── Node.js (for MCP servers)
 ├── Bun (optional — included with oh-my-opencode-slim)
@@ -362,6 +418,8 @@ Container (Debian bookworm)
 | `/home/developer/.aws` | Host bind mount (if configured) | ✅ Yes | AWS credentials/SSO cache |
 | `/home/developer/.local/share/opencode` | Named volume `devbox-data` | ✅ Yes | Session history, memory |
 | `/home/developer/.local/share/uv` | Named volume `devbox-uv` (if configured) | ✅ Yes | Python installs, uv tool installs |
+| `/home/developer/.rustup` | Named volume `devbox-rustup` (if configured) | ✅ Yes | Rust toolchains |
+| `/home/developer/.cargo` | Named volume `devbox-cargo` (if configured) | ✅ Yes | Cargo binaries, registry cache |
 | `/home/developer/.config/opencode` | Host bind mount (if configured) | ✅ Yes | opencode.json, oh-my-opencode-slim.json, skills |
 
 **opencode config** (`opencode.json`) is auto-generated from `OPENCODE_PROVIDER` on each start. It sets provider and model only — no MCP servers. To persist config changes and use custom settings, mount the config directory from the host (see Custom opencode config above).