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/lib/kernel-chat.ts

@@ -59,6 +59,7 @@ export function installChatMethods(ClientClass: { prototype: KernelClient }): vo
       thinking_enabled?: boolean;
       reasoning_effort?: string;
       plan_mode?: boolean;
+      subagent_enabled?: boolean;
     }
   ): Promise<{ runId: string }> {
     const runId = crypto.randomUUID();
@@ -185,6 +186,7 @@ export function installChatMethods(ClientClass: { prototype: KernelClient }): vo
           thinkingEnabled: opts?.thinking_enabled,
           reasoningEffort: opts?.reasoning_effort,
           planMode: opts?.plan_mode,
+          subagentEnabled: opts?.subagent_enabled,
         },
       });
     } catch (err: unknown) {