refactor(hands): 移除空壳 Hand — Whiteboard/Slideshow/Speech (Phase 5)

删除 3 个仅含 UI 占位的 Hand，清理 Rust 实现与前端引用：
- Rust: whiteboard.rs(422行) + slideshow.rs(797行) + speech.rs(442行)
- 前端: WhiteboardCanvas + SlideshowRenderer + speech-synth + 相关类型/常量
- 配置: 3 个 HAND.toml
- 净减 ~5400 行，Hands 9→6(启用) + Quiz/Browser/Researcher/Collector/Clip/Twitter/Reminder

crates/zclaw-kernel/src/kernel/mod.rs

@@ -27,7 +27,7 @@ use crate::config::KernelConfig;
 use zclaw_memory::MemoryStore;
 use zclaw_runtime::{LlmDriver, ToolRegistry, tool::SkillExecutor};
 use zclaw_skills::SkillRegistry;
-use zclaw_hands::{HandRegistry, hands::{BrowserHand, SlideshowHand, SpeechHand, QuizHand, WhiteboardHand, ResearcherHand, CollectorHand, ClipHand, TwitterHand, ReminderHand, quiz::LlmQuizGenerator}};
+use zclaw_hands::{HandRegistry, hands::{BrowserHand, QuizHand, ResearcherHand, CollectorHand, ClipHand, TwitterHand, ReminderHand, quiz::LlmQuizGenerator}};
 
 pub use adapters::KernelSkillExecutor;
 pub use messaging::ChatModeConfig;
@@ -93,10 +93,7 @@ impl Kernel {
         let quiz_model = config.model().to_string();
         let quiz_generator = Arc::new(LlmQuizGenerator::new(driver.clone(), quiz_model));
         hands.register(Arc::new(BrowserHand::new())).await;
-        hands.register(Arc::new(SlideshowHand::new())).await;
-        hands.register(Arc::new(SpeechHand::new())).await;
         hands.register(Arc::new(QuizHand::with_generator(quiz_generator))).await;
-        hands.register(Arc::new(WhiteboardHand::new())).await;
         hands.register(Arc::new(ResearcherHand::new())).await;
         hands.register(Arc::new(CollectorHand::new())).await;
         hands.register(Arc::new(ClipHand::new())).await;