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/UnityConnectSettings.asset

@@ -0,0 +1,40 @@
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+%TAG !u! tag:unity3d.com,2011:
+--- !u!310 &1
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+  m_DashboardUrl: https://dashboard.unity3d.com
+  m_TestInitMode: 0
+  InsightsSettings:
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+    m_Enabled: 0
+  CrashReportingSettings:
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+    m_EventUrl: https://perf-events.cloud.unity3d.com
+    m_EnableCloudDiagnosticsReporting: 0
+    m_LogBufferSize: 10
+    m_CaptureEditorExceptions: 1
+  UnityPurchasingSettings:
+    m_Enabled: 0
+    m_TestMode: 0
+  UnityAnalyticsSettings:
+    m_Enabled: 0
+    m_TestMode: 0
+    m_InitializeOnStartup: 1
+    m_PackageRequiringCoreStatsPresent: 0
+  UnityAdsSettings:
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+    m_InitializeOnStartup: 1
+    m_TestMode: 0
+    m_IosGameId: 
+    m_AndroidGameId: 
+    m_GameIds: {}
+    m_GameId: 
+  PerformanceReportingSettings:
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