refactor: Enhance file attachment handling and UI components

- Updated the file attachment service to utilize a new LocalAttachment class, improving the management of file metadata such as display names.
- Refactored methods for picking and uploading files to accommodate the new LocalAttachment structure, ensuring consistent handling of file attributes.
- Improved the chat page to validate and manage file attachments more effectively, enhancing user experience during file uploads.
- Added functionality for image previews in the file attachment widget, allowing users to see selected images before sending.
- Introduced a remove button for attachments, improving usability by enabling users to easily discard unwanted files.

pubspec.yaml

@@ -99,7 +99,7 @@ flutter:
 flutter_native_splash:
   # Splash background matches the light theme; `color_dark` handles dark mode.
   color: "#FFFFFF"
-  color_dark: "#0B0E14"
+  color_dark: "#0A0A0A"
   # Image to display on the splash screen
   image: assets/icons/icon.png
 
@@ -107,7 +107,7 @@ flutter_native_splash:
   # Android specific settings
   android_12:
     color: "#FFFFFF"
-    color_dark: "#0B0E14"
+    color_dark: "#0A0A0A"
   
   # Web specific settings
   web: false