Research lab planet: spawn more often, block extractors, clearer feedback (#74, #75, #76)

#74: RESEARCH_LAB_CHANCE raised from 0.08 to 0.16 - research points
gate mid/late skill-tree nodes and vessel/lab research now (#63), so
0.08 was too scarce for how central they'd become to progression.

#75: an extractor placed on a research_lab planet would sit on an
empty resource id forever, since it yields nothing by design. Refused
in BuildController's placement confirm, with the same "explain the
refusal" idiom every other build gate uses. register_capture_points()
gained an optional definition_id parameter so the refusal/reward logic
can tell a research_lab planet apart without threading an extra
argument through every existing caller.

#76: conquering a research_lab awarded a research point with no
on-screen acknowledgement beyond a HUD number the player has no reason
to be watching at that exact moment. CaptureLabel's existing
"CONQUERED" flash now names the reward directly on a research_lab.

test_extractor_building.gd and test_planet_conquest_gate.gd both use a
"first planet chunk found" scan with no regard for definition_id; in
this world's fixed seed that chunk happens to be a research_lab, so
#75's new gate started refusing their otherwise-unrelated extractor
placement checks. Both now skip a research_lab chunk when picking
their target, same as test_research_lab_extractor_gate.gd does on
purpose for its own dedicated coverage of that refusal.

tests/test_research_lab_extractor_gate.gd

@@ -0,0 +1,114 @@
+extends SceneTree
+
+# Headless gameplay test: run with
+#   godot --headless -s res://tests/test_research_lab_extractor_gate.gd
+# Forgejo #75: a research_lab planet yields no resources at all (#63) - an
+# extractor placed there would sit on an empty resource id forever. The
+# build menu must refuse the placement and explain why, the same "explain
+# the refusal" idiom used for every other build gate. Mirrors
+# test_extractor_building.gd's own chunk-discovery/settle/confirm shape.
+
+var main_scene: Node
+var fleet: Node
+var game_state: Node
+var controller: Node
+var target_chunk: Vector2i
+var target_planet_id: String
+var stage: int = 0
+var elapsed: float = 0.0
+
+
+func _initialize() -> void:
+	var found: bool = false
+	for x in range(-40, 40):
+		for y in range(-40, 40):
+			var chunk: Vector2i = Vector2i(x, y)
+			if not WorldGen.has_planet_at_chunk(chunk):
+				continue
+			if WorldGen.planet_data_at_chunk(chunk).definition_id == "research_lab":
+				target_chunk = chunk
+				found = true
+				break
+		if found:
+			break
+	if not found:
+		print("TEST_RESEARCH_LAB_EXTRACTOR_GATE: FAIL (no research_lab chunk found to test with)")
+		quit(1)
+		return
+
+	game_state = root.get_node("GameState")
+	game_state.rocks = 200
+	game_state.buildings.clear()
+	game_state.extractors.clear()
+	game_state.planet_capture.clear()
+	target_planet_id = "chunk:%d:%d" % [target_chunk.x, target_chunk.y]
+	# This test is about the resource-id gate, not conquest itself (see
+	# test_planet_conquest_gate) - pre-conquer the target directly.
+	game_state.register_capture_points(target_planet_id, 1, "research_lab")
+	game_state.mark_point_captured(target_planet_id, 0)
+	game_state.reset_progression()
+	for node in GameState.SKILL_TREE:
+		game_state.unlocked.append(node.id)
+
+	main_scene = load("res://Main.tscn").instantiate()
+	root.add_child(main_scene)
+	fleet = main_scene.get_node("Fleet")
+	controller = main_scene.get_node("BuildController")
+
+
+func _process(delta: float) -> bool:
+	elapsed += delta
+	match stage:
+		0:
+			main_scene.get_node("AsteroidField").set_process(false)
+			main_scene.get_node("EnemySpawner").set_process(false)
+
+			var near: Vector2 = WorldGen.chunk_origin(target_chunk) + Vector2.ONE * WorldGen.CHUNK_SIZE * 0.5
+			for ship in fleet.ships:
+				ship.position = near
+			fleet.move_to(near)
+			elapsed = 0.0
+			stage = 1
+			return false
+		1:
+			var planet_field: Node = main_scene.get_node("PlanetField")
+			if elapsed < planet_field.check_interval + 0.2:
+				return false
+			if not planet_field.populated_chunks.has(target_chunk):
+				return _fail("the research_lab planet never spawned")
+			var planet: Node2D = planet_field.populated_chunks[target_chunk][0]
+			if String(planet.resource_type) != "":
+				return _fail("test setup error: chosen planet's resource_type is '%s', expected empty" \
+					% planet.resource_type)
+			for ship in fleet.ships:
+				ship.position = planet.position
+			fleet.move_to(planet.position)
+			elapsed = 0.0
+			stage = 2
+			return false
+		2:
+			if elapsed < 0.3:
+				return false
+			controller._on_build_pressed()
+			if not controller.build_menu.visible:
+				return _fail("the build menu did not open over the planet")
+
+			var before: int = game_state.extractors.size()
+			controller._show_building_info(GameState.BUILDING_EXTRACTOR)
+			controller._confirm_build()
+			if game_state.extractors.size() != before:
+				return _fail("an extractor was built on a research_lab planet")
+			if not ("nothing to extract" in controller.build_status.text):
+				return _fail("refusal did not explain itself, status was '%s'" % controller.build_status.text)
+			print("extractor refused on a research_lab planet, explained: '%s'" % controller.build_status.text)
+
+			print("TEST_RESEARCH_LAB_EXTRACTOR_GATE: PASS")
+			quit(0)
+			return true
+	return false
+
+
+func _fail(message: String) -> bool:
+	print("TEST_RESEARCH_LAB_EXTRACTOR_GATE: FAIL (%s)" % message)
+	quit(1)
+	return true