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/share_service.rs

@@ -132,8 +132,9 @@ impl ShareService {
     /// concurrently. This keeps RAM usage predictable (~19 MB × 2 = ~38 MB max)
     /// and avoids starving the Tokio blocking thread pool.
     async fn hash_password_async(&self, password: &str) -> Result<String, DomainError> {
-        let _permit = self.hash_semaphore.acquire().await
-            .map_err(|_| DomainError::internal_error("ShareService", "Hash semaphore closed".to_string()))?;
+        let _permit = self.hash_semaphore.acquire().await.map_err(|_| {
+            DomainError::internal_error("ShareService", "Hash semaphore closed".to_string())
+        })?;
         self.password_hasher.hash_password(password).await
     }
 }