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/PackageManagerSettings.asset

@@ -0,0 +1,43 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!114 &1
+MonoBehaviour:
+  m_ObjectHideFlags: 61
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 0}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 13964, guid: 0000000000000000e000000000000000, type: 0}
+  m_Name: 
+  m_EditorClassIdentifier: 
+  m_EnablePreviewPackages: 0
+  m_EnablePackageDependencies: 0
+  m_AdvancedSettingsExpanded: 1
+  m_ScopedRegistriesSettingsExpanded: 1
+  oneTimeWarningShown: 0
+  m_Registries:
+  - m_Id: main
+    m_Name: 
+    m_Url: https://packages.unity.com
+    m_Scopes: []
+    m_IsDefault: 1
+    m_Capabilities: 7
+  m_UserSelectedRegistryName: 
+  m_UserAddingNewScopedRegistry: 0
+  m_RegistryInfoDraft:
+    m_ErrorMessage: 
+    m_Original:
+      m_Id: 
+      m_Name: 
+      m_Url: 
+      m_Scopes: []
+      m_IsDefault: 0
+      m_Capabilities: 0
+    m_Modified: 0
+    m_Name: 
+    m_Url: 
+    m_Scopes:
+    - 
+    m_SelectedScopeIndex: 0