Implement WOPI integration for Collabora Online

- Add WOPI models (CheckFileInfoResponse, PutFileResponse, LockInfo)
- Implement WOPI handlers: CheckFileInfo, GetFile, PutFile, Lock operations
- Add file locking mechanism to prevent concurrent editing conflicts
- Add WOPI session endpoint for generating access tokens
- Add UpdateFileSize method to database
- Add WOPI routes (/wopi/files/* endpoints)
- Update Flutter document viewer to load Collabora via WOPI WOPISrc URL
- Implement WebView integration for Collabora Online viewer
- Add comprehensive logging for WOPI operations [WOPI-TOKEN], [WOPI-REQUEST], [WOPI-STORAGE], [WOPI-LOCK]

go_cloud/internal/database/db.go

@@ -659,3 +659,12 @@ func (db *DB) MarkChallengeUsed(ctx context.Context, challenge []byte) error {
 	`, challenge)
 	return err
 }
+// UpdateFileSize updates the size and last_modified timestamp of a file
+func (db *DB) UpdateFileSize(ctx context.Context, fileID uuid.UUID, size int64) error {
+	_, err := db.ExecContext(ctx, `
+		UPDATE files
+		SET size = $1, last_modified = NOW()
+		WHERE id = $2
+	`, size, fileID)
+	return err
+}