Implement Wave 1 + Wave 2 import pipeline

[kylaalsbury-nealy]

Lands the foundation and parallel-track tasks from docs/roadmap.md so researchers can drag a Studio JSON export into Assets/ and spawn a fully-componented environment with collider and prefab-substitution support.

Wave 1 - Foundation:

• F1: build/publish-core-dll.{ps1,sh} scripts + Plugins/README explaining how to drop in the netstandard2.1 OpenApparatus.Core.dll from a sibling openapparatus-core clone.
• F2: Runtime components (EnvironmentRoot, Room, Wall, RoomObjectInstance, OpeningSpec), MultiRoomEnvironmentAsset ScriptableObject + supporting data types, OpenApparatusSpace coord-handedness helper, MaterialResolver, OpenApparatusGeometry mesh wrapper.
• F3: MaterialResolver synthesises pipeline-appropriate defaults via Shader.Find when no authored .mat is present; versionDefines wire URP / HDRP detection through both asmdefs; Materials/README documents the authored-default override path.

Wave 2 - Parallel:

• A: JsonEnvironmentImporter (ScriptedImporter for .json) with v3 sniff
  • v4 schema marker discriminator, POCO mirror of the JSON schema, Newtonsoft.Json deserialisation (added as a UPM dependency), and a JsonGeometryBuilder that produces per-room floor/wall/ceiling meshes as sub-assets. Foreign .json files fall through to TextAsset.
• B: GltfEnvironmentPostprocessor recognises Room_, Room_wall, and Room_object_ node names and attaches the matching components. Best-effort start/end from mesh bounds; passage defaults to Closed unless a paired JSON wins.
• I: ColliderBuilder generates BoxCollider on each Wall (rotated to align with the segment) and one BoxCollider per Room tile, gated by MultiRoomEnvironmentAsset.ColliderMode.
• J: PrefabSubstitutionTable ScriptableObject + ReorderableList editor + PrefabSubstitutionApplicator that swaps RoomObjectInstance placeholders for researcher-supplied prefabs with position / rotation / scale overrides.
• D: Samples~/ImportedEnvironment/ with single_room.json + README, wired into package.json's samples block.
• E: Tests/Editor/ asmdef + tests for OpenApparatusSpace, JSON discriminator / importer, glTF postprocessor, collider builder, prefab substitution; GitHub Actions workflow runs edit-mode tests via game-ci/unity-test-runner against Tests/UnityProject (a minimal host that consumes the package via a relative file:// dependency).

EnvironmentSpawner ties the spawn flow together: places rooms + walls + placeholder objects, then runs PrefabSubstitutionApplicator and ColliderBuilder in that order. Asset inspector exposes ColliderMode and Substitution above the Spawn button.

Known gaps documented for follow-up:

• Plugins/OpenApparatus.Core.dll is not committed; run the publish script against the sibling openapparatus-core clone to produce it.
• single_room.glb fixture for the glTF postprocessor needs Studio export; current glTF test exercises the name-recognition logic via a synthetic GameObject hierarchy.
• JsonGeometryBuilder produces simple wall prisms without door cutouts; geometry quality is "topology-verifiable" not "presentation-ready".