Add mobile camera capture, polaroid preview, gallery save & native share

- カメラ撮影 → プレビュー(ポラロイド風白縁)→ 保存 / ネイティブ共有
- iOS / Android のネイティブ実装(共有・ギャラリー保存・FileProvider)
- iOS は共有シートのプリウォームで初回表示を軽減
- iOS Info.plist 用途説明をビルド後処理で自動付与
- Android パッケージ名ガードを有効化(ビルド前チェック)
- README を整備、.gitignore に slnx / .vscode / .utmp を追加

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ProjectSettings/DynamicsManager.asset

@@ -0,0 +1,36 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!55 &1
+PhysicsManager:
+  m_ObjectHideFlags: 0
+  serializedVersion: 13
+  m_Gravity: {x: 0, y: -9.81, z: 0}
+  m_DefaultMaterial: {fileID: 0}
+  m_BounceThreshold: 2
+  m_SleepThreshold: 0.005
+  m_DefaultContactOffset: 0.01
+  m_DefaultSolverIterations: 6
+  m_DefaultSolverVelocityIterations: 1
+  m_QueriesHitBackfaces: 0
+  m_QueriesHitTriggers: 1
+  m_EnableAdaptiveForce: 0
+  m_ClothInterCollisionDistance: 0.1
+  m_ClothInterCollisionStiffness: 0.2
+  m_ContactsGeneration: 1
+  m_LayerCollisionMatrix: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
+  m_AutoSimulation: 1
+  m_AutoSyncTransforms: 0
+  m_ReuseCollisionCallbacks: 1
+  m_ClothInterCollisionSettingsToggle: 0
+  m_ClothGravity: {x: 0, y: -9.81, z: 0}
+  m_ContactPairsMode: 0
+  m_BroadphaseType: 0
+  m_WorldBounds:
+    m_Center: {x: 0, y: 0, z: 0}
+    m_Extent: {x: 250, y: 250, z: 250}
+  m_WorldSubdivisions: 8
+  m_FrictionType: 0
+  m_EnableEnhancedDeterminism: 0
+  m_EnableUnifiedHeightmaps: 1
+  m_SolverType: 0
+  m_DefaultMaxAngularSpeed: 50