Improve world authoring workflow

world/README-WORLD-AUTHORING.md

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+# World authoring
+
+The active test world uses the human-authored starter island through
+`world/regions/starter_island_region.tscn`.
+
+## Active composition
+
+`world/test_world.tscn` owns the gameplay-wide environment, sun, world bounds,
+and below-world failsafe. `StarterIslandRegion` owns the placed island content:
+
+```text
+StarterIslandRegion
+├── Terrain
+│   ├── Visual
+│   └── Collision
+├── WaterBodies
+│   ├── Pond
+│   │   ├── VisualWater
+│   │   ├── FishingRegion
+│   │   └── RecoveryRegion
+│   └── Ocean
+│       ├── VisualWater
+│       ├── FishingRegions
+│       └── RecoveryRegions
+├── PlayerSpawn
+├── SafeRespawns
+└── Interactables
+    ├── FishingShopWorld
+    └── PelicanCoolerPerch
+```
+
+Move the meaningful feature root rather than one of its implementation
+children. Child transforms are local offsets owned by that feature.
+
+## Water bodies
+
+Select `WaterBodies/Pond` to move or resize the pond. Its transform is the
+authoritative surface position. The `surface_size`, fishing padding, recovery
+padding, and recovery depth properties update the visible water and gameplay
+coverage together. Fishing and recovery derive the surface height from the
+owned surface transform.
+
+Select `WaterBodies/Ocean` to move the surrounding water as one feature. Its
+visual, fishing lobes, and recovery lobes use local transforms beneath the
+ocean root. The existing multi-lobe footprint remains intentionally explicit;
+changing that footprint still requires editing its owned lobe children.
+
+## Placed features
+
+- `PlayerSpawn` is the authoritative initial player transform. Its rotation
+  controls initial facing.
+- Each marker under `SafeRespawns` is an authoritative recovery destination.
+  Recovery preserves the player's current facing; marker rotation is
+  intentionally not applied.
+- `Interactables/FishingShopWorld` owns the shop visual, collision,
+  interaction area, prompt, and entrance marker.
+- `Interactables/PelicanCoolerPerch` owns the complete Pelican landmark visual.
+  Pelican selling remains a Cooler action and has no world interaction area.
+- `Terrain` owns both the imported visual and generated terrain collision.
+- `BelowWorldFailsafe/Coverage` exposes the below-world recovery coverage as a
+  saved collision shape in `world/test_world.tscn`.
+
+The active `Environment`, `Sun`, and external starter-island grass material
+remain directly editable through the Inspector. Their tuning is not recreated
+by runtime scripts.
+
+## Reusable world props
+
+Use a single placed `WorldProp` root for trees, rocks, buildings, benches,
+signs, vegetation, and similar landmarks:
+
+```text
+WorldProp
+├── Visual
+└── Collision
+    └── CollisionShape3D
+```
+
+Add optional interaction areas, labels, and markers beneath the same root.
+Instance imported GLB visuals beneath `Visual`; keep gameplay collision
+Godot-owned beneath `Collision`. Place and duplicate the complete prop scene,
+not its visual child.
+
+Author reusable assets at scale `(1, 1, 1)`. Uniform root scaling is acceptable
+for provisional props when visual and collision scale together. Avoid
+non-uniform root scaling because it can deform collision and imported geometry
+unpredictably. Make mutable per-instance shapes, meshes, and materials local to
+the scene so editing one prop does not change unrelated instances.