This commit introduces "Share" and "Open in..." actions to the `PhotoViewScreen`, allowing users to share images via other apps or open them in external viewers.
**Key changes:**
- **PhotoViewer:**
- Added "Share" and "Open in..." options to the `PhotoViewScreen` dropdown menu.
- `PhotoViewViewModel`:
- Implemented `onShareClicked()` and `onOpenInClicked()` to handle these new actions.
- Added `shareRequest` StateFlow to manage image sharing intents.
- Introduced `downloadAndStoreImageToCache()` to download and cache images for sharing.
- `onImageShared()` resets `shareRequest` after sharing.
- Updated `TopBar` to include the new menu items.
- Added string resources for "Open in…" and "Share".
- **Reply UI:**
- `Reply.kt`: Title and summary text now use `TextOverflow.Ellipsis` to prevent long text from breaking the layout.
- **API Model:**
- `MessagesResponse.kt`: Added `MessagesMarkAsImportantResponse` data class to handle the response for marking messages as important.
- **Data Layer:**
- `MessagesRepositoryImpl`: Updated `markAsImportant` to correctly map the API response using `MessagesMarkAsImportantResponse`.
- **Minor:**
- `README.md`: Updated feature checklist for external viewer.
- `ApplicationModule.kt`: Added experimental Coil API opt-in.
melod1n