fix(content): put the Saignee entrance landmark where the groove is deep

The landmark sat on GROOVE_START, where the groove's end taper brings
its depth to zero, so the marker (-34 m) was below the seabed (-26.5 m)
and a probe there saw no trench. It now sits two half-widths inside the
groove, on the groove floor.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

content/sites/zone1_vigilant.tres

@@ -91,7 +91,7 @@ position_m = Vector3(0, -25, -230)
 [sub_resource type="Resource" id="Resource_u8dqp"]
 script = ExtResource("1_n3xpu")
 placement_id = &"saignee_entrance"
-position_m = Vector3(-60, -34, -140)
+position_m = Vector3(-56.978443, -35.474903, -124.287895)
 
 [sub_resource type="Resource" id="Resource_3uttw"]
 script = ExtResource("1_n3xpu")

tools/sites/zone1_vigilant_recipe.gd

@@ -19,6 +19,9 @@ const BREAK_Z := 125.0
 # The target's centre sits this far up the groove from GROOVE_END, so its 28 m hull
 # stops one groove half-width short of the end cap and rests on the flat groove floor.
 const TARGET_SET_BACK_M := 22.0
+# The groove tapers to nothing over one half-width at each end: the entrance landmark
+# sits two half-widths inside, where the groove has its full depth.
+const ENTRANCE_INSET_M := 16.0
 
 
 static func recipe() -> SiteTerrainBaker.Recipe:
@@ -70,6 +73,8 @@ static func definition(terrain: SiteTerrainData) -> DiveSiteDefinition:
 	var groove_axis := (GROOVE_END - GROOVE_START).normalized()
 	var groove_yaw := atan2(-groove_axis.y, groove_axis.x)
 	var target_xz := GROOVE_END - groove_axis * TARGET_SET_BACK_M
+	var entrance_xz := GROOVE_START + groove_axis * ENTRANCE_INSET_M
+	var entrance_m := Vector3(entrance_xz.x, field.elevation_at(entrance_xz.x, entrance_xz.y), entrance_xz.y)
 	var result := DiveSiteDefinition.new()
 	result.site_id = &"zone1_vigilant"
 	result.display_name = "Banc du Vigilant"
@@ -99,7 +104,7 @@ static func definition(terrain: SiteTerrainData) -> DiveSiteDefinition:
 		_marker(&"echine", SitePlacement.Kind.LANDMARK, Vector3(75.0, -20.0, -50.0)),
 		_marker(&"deux_freres", SitePlacement.Kind.LANDMARK, Vector3(-151.0, -18.0, -125.0)),
 		_marker(&"rides", SitePlacement.Kind.LANDMARK, Vector3(0.0, -25.0, -230.0)),
-		_marker(&"saignee_entrance", SitePlacement.Kind.LANDMARK, Vector3(-60.0, -34.0, -140.0)),
+		_marker(&"saignee_entrance", SitePlacement.Kind.LANDMARK, entrance_m),
 		_marker(&"rupture", SitePlacement.Kind.LANDMARK, Vector3(40.0, -40.0, 125.0)),
 	]
 	result.routes = [