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_terrain_edges.gd

@@ -0,0 +1,39 @@
+extends SceneTree
+## Terrain edge check: there must be no ground below the inland waterline in the
+## band just inside the boundary wall. Ground like that shows up as inland water
+## hanging over a drop (the lake water surface stops at the wall) and makes pits
+## the player can fall into and not climb out of.
+##
+## Run: godot --headless --path . --script res://tests/test_terrain_edges.gd
+
+const BAND := 10.0   # metres inside the wall to check
+
+func _initialize() -> void:
+	var terrain: Node3D = load("res://scripts/world/terrain.gd").new()
+	root.add_child(terrain)   # builds in _ready
+	_run.call_deferred(terrain)
+
+func _run(terrain: Node3D) -> void:
+	var bad := 0
+	var worst := INF
+	var worst_at := Vector2.ZERO
+	var half: float = terrain.size * 0.5
+	var x := -half
+	while x < half:
+		var z := -half
+		while z < half:
+			if terrain.inside_boundary(x, z, 0.0) and not terrain.inside_boundary(x, z, BAND):
+				var h: float = terrain.sample_height(x, z)
+				if h < terrain.water_level + 0.2:
+					bad += 1
+					if h < worst:
+						worst = h
+						worst_at = Vector2(x, z)
+			z += 1.0
+		x += 1.0
+	if bad > 0:
+		print("FAIL: %d samples near the wall are below the waterline; lowest %.1f m at (%.0f, %.0f), sea weight %.2f" % [
+			bad, worst, worst_at.x, worst_at.y, terrain.sea_weight(worst_at.x, worst_at.y)])
+	else:
+		print("PASS: ground near the wall stays above the waterline")
+	quit(1 if bad > 0 else 0)