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-tauri/src/kernel_commands/chat.rs

@@ -60,6 +60,9 @@ pub struct StreamChatRequest {
     /// Enable plan mode
     #[serde(default)]
     pub plan_mode: Option<bool>,
+    /// Enable sub-agent delegation (Ultra mode only)
+    #[serde(default)]
+    pub subagent_enabled: Option<bool>,
 }
 
 // ---------------------------------------------------------------------------
@@ -216,6 +219,7 @@ pub async fn agent_chat_stream(
             thinking_enabled: request.thinking_enabled,
             reasoning_effort: request.reasoning_effort.clone(),
             plan_mode: request.plan_mode,
+            subagent_enabled: request.subagent_enabled,
         };
 
         let rx = kernel.send_message_stream_with_prompt(