fix(thumbnails): resolve blob path instead of logical path for thumbnail generation

Since the blob storage migration (3c7c16f), thumbnail generation failed
with "No such file or directory" because the handler constructed logical
file paths that don't exist on disk. Resolve the actual blob path via
get_blob_hash() + dedup_service.blob_path() in both upload and get
thumbnail handlers. Add regression tests.

src/interfaces/api/handlers/file_handler.rs

@@ -14,7 +14,7 @@ use crate::application::ports::file_ports::OptimizedFileContent;
 use crate::application::ports::file_ports::{
     FileManagementUseCase, FileRetrievalUseCase, FileUploadUseCase,
 };
-use crate::application::ports::storage_ports::StorageUsagePort;
+use crate::application::ports::storage_ports::{FileReadPort, StorageUsagePort};
 use crate::application::ports::thumbnail_ports::ThumbnailPort;
 use crate::common::di::AppState;
 use crate::interfaces::errors::AppError;
@@ -322,8 +322,20 @@ impl FileHandler {
                 .into_response();
         }
 
-        let storage_root = state.core.path_service.get_root_path();
-        let file_path = storage_root.join(&file.path);
+        // Resolve the actual blob path on disk (not the logical file path).
+        let blob_hash = match state.repositories.file_read_repository.get_blob_hash(&id).await {
+            Ok(h) => h,
+            Err(err) => {
+                return (
+                    StatusCode::NOT_FOUND,
+                    Json(serde_json::json!({
+                        "error": format!("File content not found: {}", err)
+                    })),
+                )
+                    .into_response();
+            }
+        };
+        let file_path = state.core.dedup_service.blob_path(&blob_hash);
 
         match thumbnail_service
             .get_thumbnail(&id, thumb_size.into(), &file_path)
@@ -597,12 +609,21 @@ impl FileHandler {
             .is_supported_image(&file.mime_type)
         {
             let file_id = file.id.clone();
-            let file_path_rel = file.path.clone();
             let thumbnail_service = state.core.thumbnail_service.clone();
-            let path_service = state.core.path_service.clone();
+            let dedup_service = state.core.dedup_service.clone();
+            let file_read = state.repositories.file_read_repository.clone();
 
             tokio::spawn(async move {
-                let file_path = path_service.get_root_path().join(&file_path_rel);
+                // Resolve the actual blob path on disk (not the logical file path,
+                // which doesn't exist when using blob storage).
+                let blob_hash = match file_read.get_blob_hash(&file_id).await {
+                    Ok(h) => h,
+                    Err(e) => {
+                        tracing::warn!("Skipping thumbnails for {}: {}", file_id, e);
+                        return;
+                    }
+                };
+                let file_path = dedup_service.blob_path(&blob_hash);
                 tracing::info!("🖼️ Generating thumbnails for: {}", file_id);
                 thumbnail_service.generate_all_sizes_background(file_id, file_path);
             });