chore(config): add automated Rust install to make setup

Adds tooling/install-rust script that installs Rust via rustup if
not present, with clippy and rustfmt components. Idempotent — skips
when already installed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Makefile

@@ -33,9 +33,7 @@ setup: setup-rust setup-godot setup-tooling decisions-sync
 	@echo "Dev environment ready."
 
 setup-rust:
-	@echo "Checking Rust toolchain..."
-	@command -v cargo >/dev/null 2>&1 || { echo "Install Rust: https://rustup.rs"; exit 1; }
-	@rustup component add clippy rustfmt
+	@tooling/install-rust
 
 setup-godot:
 	@GODOT_VERSION=$(GODOT_VERSION) tooling/install-godot

docs/DEVOPS.md

@@ -22,7 +22,7 @@ Unit tests live inside their respective projects (`server/` uses `#[cfg(test)]`
 
 | Tool | Version | Purpose |
 |------|---------|---------|
-| Rust (via rustup) | stable | Server compilation, clippy, rustfmt |
+| Rust (via rustup) | stable | Server compilation, clippy, rustfmt (auto-installed by `make setup`) |
 | Godot | 4.x | Client editor and runtime (auto-installed to `~/bin/` by `make setup`) |
 | Python | 3.x | Tooling scripts, db connectors |
 | Make | any | Task runner (see below) |

tooling/install-rust

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# tooling/install-rust — Install Rust via rustup and add required components
+#
+# Usage:
+#   ./tooling/install-rust
+#
+# Installs rustup + stable toolchain if not present, then ensures
+# clippy and rustfmt components are installed. Idempotent.
+
+set -euo pipefail
+
+if command -v rustup >/dev/null 2>&1; then
+    echo "Rust already installed: $(rustc --version)"
+    rustup component add clippy rustfmt 2>/dev/null
+    echo "Components verified: clippy, rustfmt"
+    exit 0
+fi
+
+echo "Installing Rust via rustup..."
+
+if ! command -v curl >/dev/null 2>&1; then
+    echo "Error: curl is required to install Rust."
+    exit 1
+fi
+
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --component clippy rustfmt
+
+# Source cargo env for the rest of this script
+# shellcheck source=/dev/null
+. "$HOME/.cargo/env"
+
+echo "Rust installed: $(rustc --version)"
+echo "Components: clippy, rustfmt"