feat: sdk collision layer main player

[pravusjif]

Adds the CL_MAIN_PLAYER collider layer (replaces the unused CL_RESERVED2) and unifies how Raycast and TriggerArea treat ColliderLayer masks for the local player avatar.

What changed

• New layer CL_MAIN_PLAYER (value 8) — targets the local player avatar specifically.
• Additive avatar semantics — the main player is tagged with both CL_PLAYER and CL_MAIN_PLAYER; remote avatars carry only CL_PLAYER.
• Unified main-player qualification rule — both Raycast and TriggerArea now use the same constant PLAYER_QUALIFYING_BITS = CL_PLAYER | CL_MAIN_PLAYER. CL_PHYSICS, CL_POINTER, CL_CUSTOM*, and CL_NONE no longer hit / fire on the local player.
• MeshCollider / GltfContainer — masks containing CL_PLAYER or CL_MAIN_PLAYER (without CL_PHYSICS) now route to a new dedicated Unity layer SDKAvatarHit: raycast- and trigger-detectable, but the player capsule walks through (previously the collider was silently disabled). Mixing in CL_PHYSICS keeps the mesh solid against the player.
• TriggerArea optimisation — a CL_MAIN_PLAYER-only trigger now skips remote-avatar overlaps inside the MonoBehaviour via the existing TargetTransform early-out.
• Unity layer rename AllAvatars → SDKAvatarTriggerArea — the layer slot (18) is unchanged, only the name changes. The old name was misleading (no avatars actually live on that layer; it hosts the avatar-targeting TriggerArea collider). Pairs cleanly with the existing SDKEntityTriggerArea name. C# constant renamed PhysicsLayers.ALL_AVATARS → PhysicsLayers.SDK_AVATAR_TRIGGER_AREA.

Behaviour comparison

BEFORE

Mask	Raycast hits main player	TriggerArea fires for main player
CL_PLAYER	yes	yes
CL_PHYSICS	yes	no
CL_POINTER alone	yes	no
CL_CUSTOM* alone	yes	no
CL_NONE	yes	no

The two systems disagreed on every mask except CL_PLAYER. (CL_MAIN_PLAYER did not exist.)

AFTER

Mask	Raycast hits main player	TriggerArea fires for main player
CL_PLAYER	yes	yes
CL_MAIN_PLAYER	yes	yes
CL_PLAYER | CL_MAIN_PLAYER	yes	yes
CL_PHYSICS	no	no
CL_POINTER alone	no	no
CL_CUSTOM* alone	no	no
CL_NONE	no	no

The two systems now agree on every mask.

Migration note

Scenes that previously relied on CL_PHYSICS raycasts to detect the local player must now OR CL_MAIN_PLAYER (or CL_PLAYER) into their mask. Walls-and-floors physics checks that do not target the player are unchanged.

Related PRs

• feat: collision layer for main player protocol#414
• feat: collision layer for main player js-sdk-toolchain#1407
• chore: update collision layer docs docs#104