feat(@projects/@magic-civilization): ✨ lair overlay sprite-capable + larger legible fallback

- lair_overlay_renderer now loads sprites/lairs/<type_id>.png (via
  DrawHelpers.scaled_sprite_size, POI fraction 0.45) and draws it in place of
  the diamond marker when the asset is present.
- Enlarge + keep-labeled the diamond fallback (radius 18→26) so a lair is at
  least legible until the art lands.
- Sprite path is a no-op until the standin pipeline emits sprites/lairs/*
  (tracked as a follow-up objective).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/game/engine/src/rendering/lair_overlay_renderer.gd

@@ -4,9 +4,17 @@ extends Node2D
 ## Subscribes to lair-related EventBus signals and redraws on state changes.
 
 const HexUtilsScript: GDScript = preload("res://engine/src/map/hex_utils.gd")
+const DrawHelpers: GDScript = preload("res://engine/src/rendering/unit_renderer_draw.gd")
 
-## Lair marker geometry
-const MARKER_RADIUS: float = 18.0
+## Lair sprite path convention (sprites/lairs/<type_id>.png). When the art is
+## present it replaces the diamond marker; generated by the standin pipeline.
+const LAIR_SPRITE_FORMAT: String = "sprites/lairs/%s.png"
+## Sprite size as a fraction of hex width — POI scale, smaller than a unit (0.6)
+## but clearly readable. Mirrors the unit/city sprite-fraction convention.
+const LAIR_SPRITE_TILE_FRACTION: float = 0.45
+
+## Lair marker geometry (fallback when no sprite asset is present)
+const MARKER_RADIUS: float = 26.0
 const MARKER_OUTLINE_WIDTH: float = 2.0
 const MARKER_OUTLINE_COLOR: Color = Color(0.1, 0.1, 0.1, 0.85)
 
@@ -26,6 +34,8 @@ const EXCLUDED_TYPES: Array[String] = ["village", "ruin"]
 
 ## Cached lair display data: position (Vector2i) -> { "type_id": String, "tier": int }
 var _lairs: Dictionary = {}
+## Cached lair textures by type_id (null when no sprite asset exists yet).
+var _sprite_cache: Dictionary = {}
 
 
 func _ready() -> void:
@@ -80,10 +90,14 @@ func _draw() -> void:
 		var tier: int = data.get("tier", 1)
 		var type_id: String = data.get("type_id", "")
 		var pixel: Vector2 = HexUtilsScript.axial_to_pixel(pos) + HexUtilsScript.hex_center
-		var color: Color = _tier_color(tier)
 
-		# Draw diamond marker (rotated square)
-		_draw_diamond(pixel, MARKER_RADIUS, color)
+		# Real lair sprite when present; diamond marker as missing-asset fallback.
+		var sprite: Texture2D = _lair_sprite(type_id)
+		if sprite != null:
+			var draw_size: Vector2 = DrawHelpers.scaled_sprite_size(sprite, LAIR_SPRITE_TILE_FRACTION)
+			draw_texture_rect(sprite, Rect2(pixel - draw_size * 0.5, draw_size), false)
+		else:
+			_draw_diamond(pixel, MARKER_RADIUS, _tier_color(tier))
 
 		# Draw tier label above marker
 		var tier_name: String = _get_tier_name(tier)
@@ -92,6 +106,13 @@ func _draw() -> void:
 		_draw_tier_label(pixel, tier_name)
 
 
+func _lair_sprite(type_id: String) -> Texture2D:
+	## Load + cache the lair sprite by type_id; null until the art asset exists.
+	if not _sprite_cache.has(type_id):
+		_sprite_cache[type_id] = ThemeAssets.load_sprite(LAIR_SPRITE_FORMAT % type_id, false)
+	return _sprite_cache[type_id] as Texture2D
+
+
 func _draw_diamond(center: Vector2, radius: float, color: Color) -> void:
 	## Draw a diamond (rotated square) as the lair marker.
 	var points: PackedVector2Array = PackedVector2Array([