android: shows and attaches files, and the share sheet takes images

The phone downloaded every attachment and drew none of them, so a photo note
looked empty. Now:

- Cards show a note's first image and name its other files; the editor shows
  every image at full width and every file as a row. Tapping one opens it in
  whatever app handles its type (a cache copy under its real name, through a
  FileProvider that serves only those copies). Each can be removed, and a file
  the server refused says why under it.
- The editor's toolbar has an Attach button (any type, several at once). Files
  are stored on the phone straight away and upload on the next sync that
  reaches a server, through the core's step-6 path. Link previews show in the
  editor too, and can be dismissed.
- Share → Inkwell accepts one or several images, with or without a caption,
  finishing #1899's deferred image/* target.
- The FFI gains add_attachment, delete_attachment, delete_preview and
  blob_path. The sync summary counts uploads and failed uploads.

Images decode at the size they are drawn (BitmapFactory sampling plus EXIF
rotation, small LRU cache), so no image library is added. Files over 50 MB are
refused on the phone before they are read whole into memory.

Task #5169.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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

@@ -59,6 +59,20 @@
     <string name="editor_restore">Restore</string>
     <string name="editor_cancel">Cancel</string>
 
+    <!-- Attachments. A file is stored on the phone at once and uploaded on a later
+         sync, so nothing here talks about the network. -->
+    <string name="editor_attach">Attach a file</string>
+    <string name="attach_remove">Remove attachment</string>
+    <string name="attach_unnamed">Unnamed file</string>
+    <string name="attach_more">+%1$d more</string>
+    <string name="attach_refused">Not uploaded: %1$s</string>
+    <string name="attach_too_large">%1$s is over %2$d MB, too large to attach from the phone.</string>
+    <string name="attach_unreadable">Couldn\'t read %1$s.</string>
+    <string name="attach_not_here">This file hasn\'t downloaded to this phone yet. Sync, then try again.</string>
+    <string name="attach_no_app">No app on this phone opens this kind of file.</string>
+    <string name="attach_open_failed">Couldn\'t open the file: %1$s</string>
+    <string name="preview_remove">Remove link preview</string>
+
     <!-- Deleting for good is the only thing in the app that cannot be undone, so
          the copy says exactly that rather than asking "Are you sure?". -->
     <string name="editor_delete_forever">Delete forever</string>
@@ -247,6 +261,14 @@
         <item quantity="one">%d attachment didn\'t download — it\'ll retry on the next sync.</item>
         <item quantity="other">%d attachments didn\'t download — they\'ll retry on the next sync.</item>
     </plurals>
+    <plurals name="sync_summary_uploaded">
+        <item quantity="one">uploaded %d file</item>
+        <item quantity="other">uploaded %d files</item>
+    </plurals>
+    <plurals name="sync_summary_upload_failed">
+        <item quantity="one">%d file didn\'t upload. If the server refused it, its note says why; otherwise it\'ll retry.</item>
+        <item quantity="other">%d files didn\'t upload. Any the server refused say why on their note; the rest will retry.</item>
+    </plurals>
 
     <!-- Errors -->
     <string name="error_dismiss">Dismiss</string>