fix: resolve clippy warnings and rustfmt issues for CI compliance

Fix all clippy lints (collapsible if, clone on Copy, needless borrow,
redundant bindings, unused params) and apply rustfmt across the codebase.
Update test mocks to match Uuid-based trait signatures.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/application/ports/thumbnail_ports.rs

@@ -89,11 +89,7 @@ pub trait ThumbnailPort: Send + Sync + 'static {
     /// Returns `None` if no cached thumbnail exists on disk or in memory.
     /// Used for non-image file types (videos) where thumbnails are
     /// generated client-side and uploaded.
-    async fn get_cached_thumbnail(
-        &self,
-        file_id: &str,
-        size: ThumbnailSize,
-    ) -> Option<Bytes>;
+    async fn get_cached_thumbnail(&self, file_id: &str, size: ThumbnailSize) -> Option<Bytes>;
 
     /// Store an externally-generated thumbnail (e.g. client-side video frame).
     ///