Add black hole planet and dark matter resource (#55)

A rare, deterministically-seeded landable body yielding a fourth
resource, dark matter, obtainable only through an extractor - never a
surface pickup. Reuses every existing generic system (resource/planet
definitions, surface profiles, extractor/transporter pipeline) with no
type-switch branching.

Also fixes a latent conquest-gating gap: a surface profile with no
authored PlanetSetup (like the black hole's "void") never registered
capture points at all, permanently blocking extractor placement.
register_capture_points() now treats zero required points as vacuously
conquered, and PlanetSurfaceController registers that zero-point state
explicitly when no setup exists.

PlanetSurfaceController.gd

@@ -65,6 +65,16 @@ func _compose_surface(profile: Resource) -> void:
 		var setup_host: Node = SETUP_HOST_SCENE.instantiate()
 		feature_host.add_child(setup_host)
 		setup_host.apply_setup(setup)
+	else:
+		# No PlanetSetup exists for this profile at all (#55: "void" has
+		# none authored) - register zero required points directly, rather
+		# than leaving this planet's conquest state unregistered forever.
+		# capture_state()'s fallback for an unregistered planet_id defaults
+		# to conquered=false (see test_planet_conquest_gate.gd's own "a
+		# fresh planet reported conquered" check), which would otherwise
+		# permanently block extractor placement here - register_capture_
+		# points() treats a total of 0 as vacuously already conquered.
+		GameState.register_capture_points(GameState.planet_id, 0)
 
 
 func _on_exit_pressed() -> void: