Add research lab planets and research points (#63)

WorldGen.gd

@@ -22,6 +22,10 @@ const GAS_GIANT_THRESHOLD: float = 0.55
 # chance independent of biome - not a second smooth region to tune against
 # the first.
 const BLACK_HOLE_CHANCE: float = 0.05
+# #63: findable without excessive exploration - research points gate mid/
+# late skill-tree nodes and vessel research, so a player needs to run into
+# one of these reasonably often, not just as a rare curiosity.
+const RESEARCH_LAB_CHANCE: float = 0.08
 
 # A predictable early gas source for play-testing. The origin chunk is
 # deterministically normal space. Its explicit in-chunk position puts it
@@ -95,6 +99,8 @@ static func planet_data_at_chunk(chunk: Vector2i) -> Dictionary:
 	# roll doesn't shift which random values any LATER draw (planet_name,
 	# below) consumes for chunks that would have existed before it.
 	var black_hole_roll: float = rng.randf()
+	# Same principle, its own independent roll (#63).
+	var research_lab_roll: float = rng.randf()
 	# A stable per-chunk roll makes gas giants persistent landmarks rather
 	# than a different resource whenever the scene reloads.
 	var gas_giant: bool = guaranteed_nearby_giant or biome_at_chunk(chunk) == Biome.SPACE
@@ -104,6 +110,8 @@ static func planet_data_at_chunk(chunk: Vector2i) -> Dictionary:
 	# that chunk's whole purpose is to always be the same reachable source.
 	if not guaranteed_nearby_giant and black_hole_roll < BLACK_HOLE_CHANCE:
 		definition_id = PLANET_DEFINITIONS.BLACK_HOLE_ID
+	elif not guaranteed_nearby_giant and research_lab_roll < RESEARCH_LAB_CHANCE:
+		definition_id = PLANET_DEFINITIONS.RESEARCH_LAB_ID
 	var definition: Resource = PLANET_DEFINITIONS.get_definition(definition_id)
 	var names: PackedStringArray = definition.names
 	var planet_name: String = names[rng.randi() % names.size()]