Add invisible edge barrier and fix an out-of-bounds POI

We only ever built the inner region-to-region borders, never a wall
at the island's own outer rim (girdle) — nothing stopped the player
walking off into the (collision-less) pavilion below. Added
_build_edge_barrier(): 6 invisible BoxShape3D walls along the girdle
chords.

Also found the actual bug behind "one POI is outside": a facet's true
outer boundary is a straight hexagon chord, not an arc, so its usable
radius varies with angle — girdle_radius only at the two corners,
dropping to girdle_radius*cos(30°) (~87%) at the facet's own bisector.
Ort6 was placed at exactly the bisector angle with radius 44, just
past the true edge (~43.3 there) despite being "inside" the naive
[table_radius, girdle_radius] range. Moved it to angle 38°/radius 36,
comfortable inside the true boundary at that angle.

Verified headless: pushing the player outward with constant velocity
for 3 simulated seconds pins it at radius 42.64 (never crosses the
~43.3 true edge), settled and on_floor=true throughout. Re-verified
the POI/gate group logic still passes after moving Ort6.

main.tscn

@@ -232,7 +232,7 @@ poi_name = "Ort 5"
 marker_color = Color(0.2, 0.5, 1, 1)
 
 [node name="Ort6" parent="." instance=ExtResource("5_lquwl") groups=["region1_pois"]]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 38.1, -4.471, 22.0)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 28.37, -3.1, 22.17)
 poi_name = "Ort 6"
 marker_color = Color(0.7, 0.3, 0.9, 1)
 

terrain.gd

@@ -47,6 +47,7 @@ func _ready() -> void:
 	_build_crown()
 	_build_pavilion()
 	_build_region_borders()
+	_build_edge_barrier()
 
 func _hex_angle(k: int) -> float:
 	return deg_to_rad(angle_offset_deg) + float(k) / 6.0 * TAU
@@ -220,3 +221,35 @@ func _spawn_border_prop(parent: Node3D, kind: Dictionary, pos: Vector3) -> void:
 	inst.add_child(cs)
 
 	parent.add_child(inst)
+
+# ═══════════════════════════════════════════════
+# RAND-BARRIERE — unsichtbare Wand entlang der Rundiste, damit man
+# an der Außenkante der Insel nicht in den Pavillon (rein optisch,
+# ohne Kollision) hinunterfällt.
+# ═══════════════════════════════════════════════
+func _build_edge_barrier() -> void:
+	var barrier := StaticBody3D.new()
+	barrier.name = "EdgeBarrier"
+	add_child(barrier)
+
+	var girdle_pts: Array[Vector3] = []
+	for k in range(6):
+		var a := _hex_angle(k)
+		girdle_pts.append(Vector3(cos(a) * girdle_radius, -crown_drop, sin(a) * girdle_radius))
+
+	for k in range(6):
+		var k1 := (k + 1) % 6
+		var p0 := girdle_pts[k]
+		var p1 := girdle_pts[k1]
+		var length := p0.distance_to(p1)
+		var dir := (p1 - p0) / length
+		var mid := (p0 + p1) * 0.5
+
+		var box := BoxShape3D.new()
+		box.size = Vector3(1.0, 6.0, length)
+
+		var cs := CollisionShape3D.new()
+		cs.shape = box
+		cs.position = mid + Vector3(0.0, 1.0, 0.0)
+		cs.rotation.y = atan2(dir.x, dir.z)
+		barrier.add_child(cs)