M0.5: detailed scenery, mountain/sea-cliff boundary, Godot 4.7

Scenery (all procedural, seeded, no imported assets):
- Terrain shader: grass/dry grass/dirt/sand/rock strata/snow + detail normals
- 5 tree types, faceted mossy rocks, cliff outcrops, sea stacks, bushes,
  logs and stumps, batched as MultiMesh per 48 m cell
- Wind-animated grass and flowers streamed in tiles around the player
- Lake (depth-shaded water with shore foam), ocean to the horizon,
  cloud sky shader, volumetric fog, glow, softer shadows
- Swimming: float at the surface, swim-jump to climb out

World bounds:
- Steep mountain rim with an invisible wall partway up; one side opens to
  a sheer sea cliff with the wall 1 m inside the edge; whole chunk is an
  island so the mesh edge is never visible
- Respawn safety net if the player leaves the walkable area or the map
- Fix: the cliff edge now tracks the wall in the headlands (it used to
  drop away inside the wall, leaving a pit with lake water hanging over it)

Tests: tests/test_boundary.gd (24-direction escape attempt) and
tests/test_terrain_edges.gd (no ground below waterline near the wall).

Upgrades the project to Godot 4.7 (project.godot rewritten by the 4.7
importer, .uid files added) and documents it in the setup guide.

tests/test_boundary.gd

@@ -0,0 +1,57 @@
+extends SceneTree
+## Boundary test: tries to escape the valley in several directions by walking
+## and spamming jump at the mountain rim, and fails if the player ever gets past
+## the invisible wall, falls off the map, or ends up stuck below the waterline
+## (in a pit near the edge).
+##
+## Run: godot --headless --path . --fixed-fps 30 --script res://tests/test_boundary.gd
+
+const DIRECTIONS := 24
+const SECONDS_PER_TRY := 25.0
+
+func _initialize() -> void:
+	var world: Node3D = load("res://scenes/world.tscn").instantiate()
+	root.add_child(world)
+	_run.call_deferred(world)
+
+func _run(world: Node3D) -> void:
+	for _i in range(10):
+		await physics_frame
+	var terrain: Node3D = world.get_node("Terrain")
+	var player: CharacterBody3D = world.get_node("Player")
+	var failures := 0
+	var tick := 1.0 / Engine.physics_ticks_per_second
+	for i in range(DIRECTIONS):
+		var ang := TAU * i / DIRECTIONS
+		var out := Vector3(cos(ang), 0.0, sin(ang))
+		var start: Vector3 = out * (terrain.play_radius - 12.0)
+		start.y = terrain.sample_height(start.x, start.z) + 1.0
+		player.global_position = start
+		player.velocity = Vector3.ZERO
+		player.rotation = Vector3(0.0, atan2(-out.x, -out.z), 0.0)
+		Input.action_press("move_forward")
+		var escaped := false
+		var max_d := 0.0
+		var frames := int(SECONDS_PER_TRY / tick)
+		for f in range(frames):
+			if f % 12 == 0:
+				Input.action_press("jump")
+			elif f % 12 == 1:
+				Input.action_release("jump")
+			await physics_frame
+			var p := player.global_position
+			max_d = maxf(max_d, Vector2(p.x, p.z).length())
+			if not terrain.inside_boundary(p.x, p.z, -1.5) or p.y < terrain.min_height - 5.0:
+				escaped = true
+				break
+		Input.action_release("move_forward")
+		Input.action_release("jump")
+		var p := player.global_position
+		if not escaped and p.y < terrain.water_level - 0.5:
+			escaped = true   # stuck in a pit below the waterline
+		print("dir %2d (%3d deg): %s  max radius %.1f  final (%.1f, %.1f, %.1f)" % [
+			i, int(rad_to_deg(ang)), "FAILED" if escaped else "held", max_d, p.x, p.y, p.z])
+		if escaped:
+			failures += 1
+	print("RESULT: %s (%d/%d directions held)" % ["PASS" if failures == 0 else "FAIL", DIRECTIONS - failures, DIRECTIONS])
+	quit(1 if failures > 0 else 0)