feat: DeerFlow 2.0 core capabilities — Phase 1.0 + 1.1

Phase 1.0 — Butler Mode UI:
- Hide "自动化" and "技能市场" entries from sidebar navigation
- Remove AutomationPanel and SkillMarket view rendering from App.tsx
- Simplify MainViewType to only 'chat'
- Main interface is now: chat + conversation list + detail panel only

Phase 1.1 — Mode Differentiation:
- Add subagent_enabled field to ChatModeConfig (Rust), StreamChatRequest (Tauri),
  gateway-client, kernel-client, saas-relay-client, and streamStore
- TaskTool is now only registered when subagent_enabled=true (Ultra mode)
- System prompt includes sub-agent delegation instructions only in Ultra mode
- Frontend transmits subagent_enabled from ChatMode config through the full stack

This connects the 4-tier mode selector (Flash/Thinking/Pro/Ultra) to actual
backend behavioral differences — Ultra mode now truly enables sub-agent delegation.

desktop/src/store/chat/streamStore.ts

@@ -425,6 +425,7 @@ export const useStreamStore = create<StreamState>()(
           thinking_enabled: get().getChatModeConfig().thinking_enabled,
           reasoning_effort: get().getChatModeConfig().reasoning_effort,
           plan_mode: get().getChatModeConfig().plan_mode,
+          subagent_enabled: get().getChatModeConfig().subagent_enabled,
         }
       );