feat(content): bake the Jardin des Formes terrain showcase site

Five reference landforms on one 512 m field at 1 m per cell: a stratified
canyon through a mesa, a crevasse between two buttes, a boulder field on
rippled sand, two rock spurs framing a sand channel, and a sinuous
escarpment with knolls on the slope below.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

content/sites/terrain_showcase.tres

@@ -0,0 +1,21 @@
+[gd_resource type="Resource" script_class="DiveSiteDefinition" format=3]
+
+[ext_resource type="Script" path="res://game/domain/sites/site_placement.gd" id="1_vfxru"]
+[ext_resource type="Script" path="res://game/domain/sites/site_route.gd" id="2_eyncd"]
+[ext_resource type="Script" path="res://game/domain/sites/dive_site_definition.gd" id="3_gsyse"]
+[ext_resource type="Resource" path="res://content/sites/terrain_showcase_terrain.res" id="4_cdhpc"]
+
+[sub_resource type="Resource" id="Resource_1hr26"]
+script = ExtResource("1_vfxru")
+placement_id = &"vessel_anchor"
+kind = 5
+position_m = Vector3(0, -16, 0)
+
+[resource]
+script = ExtResource("3_gsyse")
+site_id = &"terrain_showcase"
+display_name = "Jardin des Formes"
+terrain = ExtResource("4_cdhpc")
+playable_bounds_m = Rect2(-220, -220, 440, 440)
+spawn_position_m = Vector3(0, -12, 0)
+placements = Array[ExtResource("1_vfxru")]([SubResource("Resource_1hr26")])