feat: improve media picking and attachment previews

Show images and GIFs fully inside chat bubbles instead of cropping them.

Split attachment flow into a visual picker for photos and videos and a separate system file picker.

Add batch visual sending with a shared caption applied to the first item until album support exists.

android/app/src/main/res/values/strings.xml

@@ -164,6 +164,8 @@
     <string name="chat_media_badge_video">Video</string>
     <string name="chat_attachment_title">Attachment</string>
     <string name="chat_attachment_gallery_file">Gallery / File</string>
+    <string name="chat_attachment_photos_videos">Photos &amp; videos</string>
+    <string name="chat_attachment_files">Files</string>
     <string name="chat_attachment_take_photo">Take photo</string>
     <string name="chat_attachment_take_video">Record video</string>
     <string name="chat_media_badge_gif">GIF</string>