fix: add server streaming support, fix pre-existing compilation errors

Server changes for client mode streaming:
- POST /api/item/ now streams body via async channel → ChannelReader
  → save_item_raw_streaming when compress=false or meta=false
- Add POST /api/item/{id}/meta endpoint for client-side metadata
- Add save_item_raw_streaming<R: Read> to SyncDataService
- Add add_item_meta to AsyncDataService

Fix pre-existing issues that were hidden behind swagger cfg gate:
- Remove #[cfg(feature = "swagger")] from item module so it compiles
  with just the server feature
- Fix parse_comma_tags usage (returns Vec, not Result)
- Fix TextDiff temporary value lifetime issue
- Fix io::Error::new → io::Error::other
- Fix ok_or_else → ok_or for Copy types
- Inline format args throughout server code
- Fix empty line after doc comment in pages.rs
- Add cfg_attr for unused_mut where mcp feature gates mutation
- Add type_complexity allow on create_auth_middleware
- Distinguish task error vs save error in spawn_blocking handlers

Co-Authored-By: andrew/openrouter/hunter-alpha <noreply@opencode.ai>

src/tests/common/test_helpers.rs

@@ -16,7 +16,7 @@ pub fn create_temp_dir() -> TempDir {
 pub fn create_temp_file_with_content(dir: &TempDir, filename: &str, content: &str) -> PathBuf {
     let file_path = dir.path().join(filename);
     let mut file = File::create(&file_path).expect("Failed to create test file");
-    write!(file, "{}", content).expect("Failed to write to test file");
+    write!(file, "{content}").expect("Failed to write to test file");
     file_path
 }
 
@@ -95,14 +95,13 @@ pub fn get_file_size(file_path: &PathBuf) -> u64 {
 
 /// Assert that a file exists
 pub fn assert_file_exists(file_path: &PathBuf) {
-    assert!(file_path.exists(), "File {:?} does not exist", file_path);
+    assert!(file_path.exists(), "File {file_path:?} does not exist");
 }
 
 /// Assert that a file does not exist
 pub fn assert_file_not_exists(file_path: &PathBuf) {
     assert!(
         !file_path.exists(),
-        "File {:?} should not exist but it does",
-        file_path
+        "File {file_path:?} should not exist but it does"
     );
 }