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/db.rs

@@ -887,7 +887,7 @@ async fn fix_seed_data(pool: &PgPool) -> SaasResult<()> {
     }
 
     // 也更新 api_tokens 表的 account_id
-    let _ = sqlx::query("UPDATE api_tokens SET account_id = $1 WHERE account_id != $1")
+    sqlx::query("UPDATE api_tokens SET account_id = $1 WHERE account_id != $1")
         .bind(primary_admin).execute(pool).await?;
 
     tracing::info!("Seed data fix completed");