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-kernel/src/export/html.rs

@@ -755,6 +755,7 @@ mod tests {
                     order: 0,
                 },
             ],
+            agents: vec![],
             metadata: ClassroomMetadata::default(),
         }
     }

crates/zclaw-kernel/src/export/markdown.rs

@@ -563,6 +563,7 @@ mod tests {
                     order: 1,
                 },
             ],
+            agents: vec![],
             metadata: ClassroomMetadata::default(),
         }
     }

crates/zclaw-kernel/src/export/pptx.rs

@@ -601,6 +601,7 @@ mod tests {
                     order: 0,
                 },
             ],
+            agents: vec![],
             metadata: ClassroomMetadata::default(),
         }
     }