refactor(crates): kernel/generation module split + DeerFlow optimizations + middleware + dead code cleanup

- Split zclaw-kernel/kernel.rs (1486 lines) into 9 domain modules
- Split zclaw-kernel/generation.rs (1080 lines) into 3 modules
- Add DeerFlow-inspired middleware: DanglingTool, SubagentLimit, ToolError, ToolOutputGuard
- Add PromptBuilder for structured system prompt assembly
- Add FactStore (zclaw-memory) for persistent fact extraction
- Add task builtin tool for agent task management
- Driver improvements: Anthropic/OpenAI extended thinking, Gemini safety settings
- Replace let _ = with proper log::warn! across SaaS handlers
- Remove unused dependency (url) from zclaw-hands

crates/zclaw-saas/src/knowledge/handlers.rs

@@ -231,13 +231,12 @@ pub async fn batch_create_items(
         }
         match service::create_item(&state.db, &ctx.account_id, req).await {
             Ok(item) => {
-                let _ = state.worker_dispatcher.dispatch(
+                if let Err(e) = state.worker_dispatcher.dispatch(
                     "generate_embedding",
                     serde_json::json!({ "item_id": item.id }),
-                ).await.map_err(|e| {
+                ).await {
                     tracing::warn!("[Knowledge] Failed to dispatch embedding for item {}: {}", item.id, e);
-                    e
-                });
+                }
                 created.push(item.id);
             }
             Err(e) => {
@@ -563,13 +562,12 @@ pub async fn import_items(
 
         match service::create_item(&state.db, &ctx.account_id, &item_req).await {
             Ok(item) => {
-                let _ = state.worker_dispatcher.dispatch(
+                if let Err(e) = state.worker_dispatcher.dispatch(
                     "generate_embedding",
                     serde_json::json!({ "item_id": item.id }),
-                ).await.map_err(|e| {
+                ).await {
                     tracing::warn!("[Knowledge] Failed to dispatch embedding for item {}: {}", item.id, e);
-                    e
-                });
+                }
                 created.push(item.id);
             }
             Err(e) => {