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-runtime/src/middleware/loop_guard.rs

@@ -41,7 +41,7 @@ impl AgentMiddleware for LoopGuardMiddleware {
         match result {
             LoopGuardResult::CircuitBreaker => {
                 tracing::warn!("[LoopGuardMiddleware] Circuit breaker triggered by tool '{}'", tool_name);
-                Ok(ToolCallDecision::Block("检测到工具调用循环，已自动终止".to_string()))
+                Ok(ToolCallDecision::AbortLoop("检测到工具调用循环，已自动终止".to_string()))
             }
             LoopGuardResult::Blocked => {
                 tracing::warn!("[LoopGuardMiddleware] Tool '{}' blocked", tool_name);