feat(client): add live server mode with make game target

Add SR_LIVE=1 environment variable to switch SimBridge from test mode
to TCP connection. Default behavior unchanged (test mode).

- sim_bridge.gd: read SR_LIVE env var instead of hardcoded test_mode
- game_state.gd: find player entity by kind.variant == "Player" instead
  of hardcoded entity_id 1 (real server assigns different IDs)
- Makefile: add 'make game' (builds server, starts it, launches client
  with SR_LIVE=1, kills server on exit) and 'make stop' helper

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

Makefile

@@ -1,6 +1,6 @@
 GODOT := $(shell command -v godot4 2>/dev/null || command -v godot 2>/dev/null)
 
-.PHONY: help setup build client server test lint ci ci-client ci-server clean \
+.PHONY: help setup build client server game stop test lint ci ci-client ci-server clean \
        decisions-sync decisions-coverage decisions-active decisions-orphan \
        db-backup db-install validate-content content-ron
 
@@ -14,7 +14,9 @@ help:
 	@echo ""
 	@echo "  make setup          Install dev dependencies (Rust, Godot, tooling)"
 	@echo "  make build          Build client and server"
-	@echo "  make client         Run the Godot client"
+	@echo "  make game           Build and run the full game (server + client)"
+	@echo "  make stop           Stop any running server instance"
+	@echo "  make client         Run the Godot client (test mode)"
 	@echo "  make server         Run the Rust simulation server"
 	@echo "  make test           Run all tests"
 	@echo "  make lint           Run all linters"
@@ -72,6 +74,19 @@ client:
 	@test -n "$(GODOT)" || { echo "Godot not found. Run 'make setup' first."; exit 1; }
 	$(GODOT) --path client
 
+game: stop build-server
+	@test -n "$(GODOT)" || { echo "Godot not found. Run 'make setup' first."; exit 1; }
+	@echo "Starting server..."
+	@cd server && cargo run &
+	@sleep 2
+	@echo "Starting client..."
+	@SR_LIVE=1 $(GODOT) --path client
+	@$(MAKE) stop
+
+stop:
+	@lsof -ti :9876 | xargs -r kill 2>/dev/null || true
+	@echo "Stopped any running server on port 9876"
+
 # --- Test ---
 
 test: test-server test-client