fix: resolve all clippy warnings and enforce cargo fmt

- display_helpers: convert module doc-comments to regular comments,
  merge identical text/markdown + text/ branches
- search_service: replace needless range loops with slice-based pagination
- folder_repository, folder_db_repository: collapse nested if statements
- favorites_pg_repository: remove unnecessary borrow on generic arg
- file_blob_read_repository: collapse 6 nested if-let blocks
- file_blob_write_repository: collapse nested if for dedup ref decrement
- chunked_upload_service: use div_ceil(), collapse 2 nested if blocks
- folder_handler: collapse nested if-let for owner check
- webdav_handler: replace 7x io::Error::new(ErrorKind::Other, ..) with
  io::Error::other(..)
- cargo fmt applied to all files

Passes: cargo clippy --all-targets --all-features -- -D warnings

src/application/services/file_management_service.rs

@@ -177,7 +177,10 @@ impl FileManagementUseCase for FileManagementService {
             .copy_folder_tree(source_folder_id, target_parent_id, dest_name)
             .await
             .map_err(|e| {
-                error!("Error copying folder tree (source: {}): {}", source_folder_id, e);
+                error!(
+                    "Error copying folder tree (source: {}): {}",
+                    source_folder_id, e
+                );
                 e
             })?;