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

world/Asteroid.gd

@@ -68,6 +68,10 @@ func take_damage(amount: int) -> bool:
 
 func shatter(drop_ore: bool) -> void:
 	AsteroidExplosionVFX.spawn(get_tree().root, position)
+	# #213. Here rather than in take_damage(), so a rock broken by a ramming
+	# hull is heard too - and NOT in AsteroidField's despawn, which frees
+	# rocks the player has simply flown away from.
+	Sfx.play(get_tree(), Sfx.ASTEROID_BREAK)
 	if drop_ore:
 		_drop_ore()
 	queue_free()