Add README screenshots: staged in-game captures between description and Downloads

- New capture tool src/test/capture_screenshots.gd (windowed, staged:
  venue overview, targeting an NPC, access inspection, radio report)
- Generated shots saved to docs/screenshots/ and embedded as a 2x2 gallery
  in README above the Downloads section

src/test/capture_screenshots.gd

@@ -0,0 +1,85 @@
+extends SceneTree
+## Dev helper: run the game windowed and capture staged screenshots for the
+## README. Saves 1600x900 PNGs to user://screenshots/.
+## Usage: godot --path . --script res://src/test/capture_screenshots.gd
+
+const OUT_DIR := "user://screenshots"
+const MAX_FRAMES := 2400 # hard cap (~40s)
+
+var frames := 0
+var gm: Node = null
+var state := 0
+var state_frames := 0
+var targeted := false
+
+func _initialize() -> void:
+	root.size = Vector2i(1600, 900)
+	var packed: PackedScene = load("res://scenes/main.tscn")
+	var inst: Node = packed.instantiate()
+	root.add_child(inst)
+
+func _process(_delta: float) -> bool:
+	frames += 1
+	# The main scene's _ready may not have run when _initialize added it;
+	# look for GameManager lazily each frame until it exists.
+	if gm == null:
+		gm = root.find_child("GameManager", true, false)
+		if gm == null and frames > 120:
+			push_error("GameManager not found")
+			quit(1)
+			return true
+	if frames > MAX_FRAMES:
+		print("timeout reached")
+		quit(0)
+		return true
+	_advance()
+	return false
+
+func _advance() -> void:
+	state_frames += 1
+	match state:
+		0:
+			# 2s overview from the guard post.
+			if state_frames >= 120:
+				_shoot("01-venue-overview.png")
+				state = 1
+				state_frames = 0
+		1:
+			# Wait for a nearby NPC so the interaction HUD has a target.
+			if gm != null and gm.npcs.size() > 0:
+				gm.call("_cycle_nearby_target")
+				targeted = true
+				state = 2
+				state_frames = 0
+		2:
+			# Give the HUD a moment, then shoot the interaction shot.
+			if state_frames >= 30:
+				_shoot("02-targeting-npc.png")
+				if targeted and gm != null:
+					gm.call("_toggle_inspection")
+				state = 3
+				state_frames = 0
+		3:
+			if state_frames >= 30:
+				_shoot("03-access-inspection.png")
+				if gm != null:
+					gm.hud.hide_inspection()
+					# Re-target (target may have moved) before opening the radio form.
+					if gm.npcs.size() > 0:
+						gm.call("_cycle_nearby_target")
+						gm.call("_open_radio", false)
+				state = 4
+				state_frames = 0
+		4:
+			if state_frames >= 30:
+				_shoot("04-radio-report.png")
+				state = 5
+				quit(0)
+
+func _shoot(file_name: String) -> void:
+	var dir := DirAccess.open("user://")
+	if dir == null or not dir.dir_exists("screenshots"):
+		dir.make_dir_recursive("screenshots")
+	var img: Image = root.get_texture().get_image()
+	var err := img.save_png(OUT_DIR.path_join(file_name))
+	print("%s -> err=%d (%dx%d)" % [file_name, err, img.get_width(), img.get_height()])