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>

client/scripts/autoloads/game_state.gd

@@ -30,16 +30,18 @@ func apply_snapshot(snapshot: Dictionary) -> void:
 
 	if snapshot.has("entities"):
 		visible_entities = snapshot.entities
-		# Derive player position from the player entity
+		# Derive player position from the entity with kind.variant == "Player"
 		var found_player := false
 		for entity in visible_entities:
-			if entity.has("entity_id") and entity.entity_id == player_entity_id:
+			if entity.has("kind") and entity.kind is Dictionary and entity.kind.get("variant") == "Player":
 				player_position = Vector2(entity.x, entity.y)
+				if entity.has("entity_id"):
+					player_entity_id = entity.entity_id
 				found_player = true
 				break
 		if not found_player and visible_entities.size() > 0:
-			push_warning("GameState: player entity_id %d not found in %d entities" % [
-				player_entity_id, visible_entities.size()])
+			push_warning("GameState: no Player entity found in %d entities" % [
+				visible_entities.size()])
 
 	if snapshot.has("tiles"):
 		visible_tiles = snapshot.tiles

client/scripts/autoloads/sim_bridge.gd

@@ -4,7 +4,7 @@ extends Node
 enum ConnectionState { DISCONNECTED, CONNECTING, CONNECTED, ERROR }
 
 var state: ConnectionState = ConnectionState.DISCONNECTED
-var test_mode: bool = true  # Enable test mode for development without Rust server
+var test_mode: bool = OS.get_environment("SR_LIVE") != "1"  # SR_LIVE=1 connects to real server
 var _test_tick: int = 0
 var _test_player_pos: Vector2i = Vector2i(10, 10)
 var _test_facing: String = "North"