Sharpen upgrades, mark the convoy's destination, and give the world sound

#204 the Beam Collimator widens the beam instead of adding range to one that
already crosses the screen; beam width becomes a per-shot vessel stat.
#205 the Energy Propulser gains three upgrades - dash recharge, dash reach,
and boosted-cruise drain - which turns three constants into vessel stats.
#206 three further doctrines carry the fleet from ten to twenty.
#207 the prologue's World Ship gets a marker, through the scanner's own
guidance arrow rather than a second one.
#208 #210 #213 #214 four new synthesised sounds: the breach opening, cargo
reaching the hold, a rock breaking, and a gas bomb blooming.
#215 building health bars are larger, plated and framed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019AJMdB7iuHuLFZM1aBu3GD

tests/_skill_menu_preview.gd

@@ -21,6 +21,8 @@ func _ready() -> void:
 	main.get_node("EnemySpawner").set_process(false)
 	main.get_node("AsteroidField").set_process(false)
 	var build: Node = main.get_node("BuildController")
+	# The tree lives on the menu, not on the controller - reaching through
+	# build.skill_tree stopped resolving at some point and this preview had
+	# been rendering an unopened menu ever since.
 	build.skill_menu.visible = true
-	build.skill_tree.selected_id = "shipyards"
-	build._refresh_skill_menu("shipyards")
+	build.skill_menu.refresh("shipyards")