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/modes/server/api/common.rs

@@ -10,7 +10,7 @@ pub struct ResponseBuilder;
 impl ResponseBuilder {
     pub fn json<T: Serialize>(data: T) -> Result<Response, StatusCode> {
         let json = serde_json::to_vec(&data).map_err(|e| {
-            log::warn!("Failed to serialize response: {}", e);
+            log::warn!("Failed to serialize response: {e}");
             StatusCode::INTERNAL_SERVER_ERROR
         })?;
 
@@ -19,7 +19,7 @@ impl ResponseBuilder {
             .header(header::CONTENT_LENGTH, json.len().to_string())
             .body(axum::body::Body::from(json))
             .map_err(|e| {
-                log::warn!("Failed to build response: {}", e);
+                log::warn!("Failed to build response: {e}");
                 StatusCode::INTERNAL_SERVER_ERROR
             })
     }
@@ -30,7 +30,7 @@ impl ResponseBuilder {
             .header(header::CONTENT_LENGTH, content.len().to_string())
             .body(axum::body::Body::from(content.to_vec()))
             .map_err(|e| {
-                log::warn!("Failed to build response: {}", e);
+                log::warn!("Failed to build response: {e}");
                 StatusCode::INTERNAL_SERVER_ERROR
             })
     }