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/_intro_marker_preview.gd

@@ -0,0 +1,21 @@
+extends Node2D
+
+# Preview, not a test - #207's destination marker during the prologue. The
+# convoy is flying north toward a World Ship 16000 units away that is never
+# on screen, so this renders the RUN beat, where the player is flying and
+# the marker is the only thing saying where.
+#
+#   bash tests/screenshot.sh res://tests/_intro_marker_preview.tscn shots/intro_marker.png 3 720x1280
+
+
+func _ready() -> void:
+	GameState.reset_new_game()
+	var main: Node = load("res://world/Main.tscn").instantiate()
+	add_child(main)
+	main.get_node("AsteroidField").set_process(false)
+	main.get_node("EnemySpawner").set_process(false)
+	# BRIEF has already run inside Main's _ready(), which is what spawns the
+	# convoy and names the destination; step on to the beat where the convoy
+	# is actually under way.
+	var director: Node = main.get_node("IntroDirector")
+	director._begin(1)