fix(taildrop): restore incoming file progress notifications

The io.Copy in PutFile was writing directly to wc, bypassing the
incomingFile wrapper whose Write method increments f.copied and fires
a throttled sendFileNotify on progress. As a result, notifyIncomingFiles
on the JS side only ever fired once (on completion) with received=0,
making progress UI impossible. The original inFile wrapping was lost
during the Android SAF refactor.

Also surface the PartialFile.Done flag through jsIncomingFile so JS can
distinguish the final "transfer complete" notification from in-progress
updates.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

feature/taildrop/send.go

@@ -134,8 +134,9 @@ func (m *manager) PutFile(id clientID, baseName string, r io.Reader, offset, len
 		}
 	}
 
-	// Copy the contents of the file to the writer.
-	copyLength, err := io.Copy(wc, r)
+	// Copy via inFile (which wraps wc) so [incomingFile.Write] can track
+	// progress and fire periodic sendFileNotify callbacks.
+	copyLength, err := io.Copy(inFile, r)
 	if err != nil {
 		return 0, m.redactAndLogError("Copy", err)
 	}