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/infrastructure/services/image_transcode_service.rs

@@ -258,11 +258,7 @@ impl ImageTranscodeService {
                 original_size,
                 transcoded_size
             );
-            return Ok((
-                original_content,
-                original_mime.to_string(),
-                false,
-            ));
+            return Ok((original_content, original_mime.to_string(), false));
         }
 
         let saved = original_size - transcoded_size;