feat: 보스 가림 시 플레이어 외곽선 표시

- PlayerOcclusionOutline: 보스(Enemy 레이어)가 플레이어를 가릴 때 외곽선 활성화
- Outline.shader: URP 법선 확장 외곽선 셰이더 (Fresnel 기반 알파)
- 외곽선용 별도 SkinnedMeshRenderer를 자식 GameObject에 생성
- ObstacleTransparencyController: Enemy 레이어 장애물 숨김 제외
- PlayerCamera: PlayerOcclusionOutline 초기화 연동

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Assets/_Game/Shaders/Outline.shader

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+Shader "Hidden/Colosseum/Outline"
+{
+    Properties
+    {
+        _OutlineWidth("Width", Range(0.001, 0.1)) = 0.02
+        _OutlineColor("Color", Color) = (1, 1, 1, 1)
+    }
+
+    SubShader
+    {
+        Tags
+        {
+            "RenderType" = "Transparent"
+            "Queue" = "Overlay"
+            "RenderPipeline" = "UniversalPipeline"
+        }
+
+        ZWrite Off
+        ZTest Always
+        Cull Front
+        Blend SrcAlpha OneMinusSrcAlpha
+
+        Pass
+        {
+            HLSLPROGRAM
+            #pragma vertex vert
+            #pragma fragment frag
+            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
+
+            CBUFFER_START(UnityPerMaterial)
+                float _OutlineWidth;
+                float4 _OutlineColor;
+            CBUFFER_END
+
+            struct Attributes
+            {
+                float3 positionOS : POSITION;
+                float3 normalOS : NORMAL;
+            };
+
+            struct Varyings
+            {
+                float4 positionCS : SV_POSITION;
+                float outlineAlpha : TEXCOORD0;
+            };
+
+            Varyings vert(Attributes input)
+            {
+                Varyings output;
+
+                float3 normalWS = TransformObjectToWorldNormal(input.normalOS);
+                float3 positionWS = TransformObjectToWorld(input.positionOS);
+                float3 viewDir = normalize(GetWorldSpaceViewDir(positionWS));
+
+                float NdotV = dot(normalWS, viewDir);
+                output.outlineAlpha = saturate(1.0 + NdotV);
+
+                positionWS += normalWS * _OutlineWidth * output.outlineAlpha;
+
+                output.positionCS = TransformWorldToHClip(positionWS);
+                return output;
+            }
+
+            half4 frag(Varyings input) : SV_Target
+            {
+                float alpha = _OutlineColor.a * pow(input.outlineAlpha, 3.0);
+                return half4(_OutlineColor.rgb, alpha);
+            }
+            ENDHLSL
+        }
+    }
+
+    FallBack Off
+}

Assets/_Game/Shaders/Outline.shader.meta

@@ -0,0 +1,9 @@
+fileFormatVersion: 2
+guid: 38b277215185d2a71b39fc85259575aa
+ShaderImporter:
+  externalObjects: {}
+  defaultTextures: []
+  nonModifiableTextures: []
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: