perf: Arc<AppState>, streaming PROPFIND, spawn_blocking SHA-256

- Issue #4: Wrap AppState in Arc — eliminates 42 Arc::clone + 16 String::clone per request
- Issue #2: Reject Depth:infinity with 403 + streaming XML with paginated DB queries
- Issue #5: Move chunked upload assembly (SHA-256 hash-on-write) to spawn_blocking
- Remove ~270 lines dead code from di.rs (unused builders, Default impl, stubs)
- Clean up unused tokio imports in chunked_upload_service.rs

src/interfaces/api/handlers/file_handler.rs

@@ -13,12 +13,13 @@ use std::collections::HashMap;
 use crate::application::ports::file_ports::OptimizedFileContent;
 use crate::common::di::AppState;
 use crate::interfaces::middleware::auth::{AuthUser, OptionalUserId};
+use std::sync::Arc;
 
 /**
  * Type aliases for dependency injection state.
  */
 /// Global application state for dependency injection
-type GlobalState = AppState;
+type GlobalState = Arc<AppState>;
 
 /**
  * API handler for file-related operations.