chore(config): add automated Godot download to make setup

Adds tooling/install-godot script that downloads the Godot binary
from GitHub releases to ~/bin/godot4. Skips download when the
correct version is already installed. Supports Linux x86_64/arm64
and macOS. GODOT_VERSION defaults to 4.6 and is overridable.

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

Makefile

@@ -1,6 +1,10 @@
 .PHONY: help setup build client server test lint ci ci-client ci-server clean \
        decisions-sync decisions-coverage decisions-active decisions-orphan
 
+# --- Configuration ---
+
+GODOT_VERSION ?= 4.6
+
 # Default
 help:
 	@echo "The Settled Reach — Development Commands"
@@ -20,6 +24,8 @@ help:
 	@echo "  make decisions-coverage Decision-to-ticket coverage by domain"
 	@echo "  make decisions-active   List active decisions"
 	@echo "  make decisions-orphan   Decisions without implementing tickets"
+	@echo ""
+	@echo "  GODOT_VERSION=4.6 make setup   Override Godot version"
 
 # --- Setup ---
 
@@ -32,12 +38,13 @@ setup-rust:
 	@rustup component add clippy rustfmt
 
 setup-godot:
-	@echo "Checking Godot..."
-	@command -v godot4 >/dev/null 2>&1 || command -v godot >/dev/null 2>&1 || { echo "Install Godot 4: https://godotengine.org"; exit 1; }
+	@GODOT_VERSION=$(GODOT_VERSION) tooling/install-godot
 
 setup-tooling:
 	@echo "Checking tooling dependencies..."
 	@command -v python3 >/dev/null 2>&1 || { echo "Install Python 3"; exit 1; }
+	@command -v curl >/dev/null 2>&1 || { echo "Install curl (required for Godot download)"; exit 1; }
+	@command -v unzip >/dev/null 2>&1 || { echo "Install unzip (required for Godot download)"; exit 1; }
 
 # --- Build ---