feat: deliverables 3-6 — cold start, simple mode UI, bridge tests, docs

Deliverable 3 — Cold Start Flow:
- New: use-cold-start.ts — cold start detection + greeting management
- Default Chinese greeting for hospital admin users
- Phase tracking: idle → greeting_sent → waiting_response → completed

Deliverable 4 — Simple Mode UI:
- New: uiModeStore.ts — 'simple'|'professional' mode with localStorage
- New: SimpleTopBar.tsx — minimal top bar with mode toggle
- Modified: App.tsx — dual layout rendering based on UI mode
- Modified: ChatArea.tsx — compact prop hides advanced controls
- Default: 'simple' mode for zero-barrier first experience

Deliverable 5 — Tauri Bridge Integration Tests:
- New: tauri-bridge.integration.test.ts — 14 test cases
- Covers: cold start, chat flow, persistence, memory, butler, UI mode, e2e
- 14/14 passing

Deliverable 6 — Release Documentation:
- New: installation-guide.md — user-facing install guide (Chinese, no jargon)
- New: hospital-deployment.md — IT admin deployment guide (Docker, GPO, SCCM)

desktop/src/components/ChatArea.tsx

@@ -49,7 +49,7 @@ const DEFAULT_MESSAGE_HEIGHTS: Record<string, number> = {
 // Threshold for enabling virtualization (messages count)
 const VIRTUALIZATION_THRESHOLD = 100;
 
-export function ChatArea() {
+export function ChatArea({ compact }: { compact?: boolean }) {
   const {
     messages, isStreaming, isLoading,
     sendMessage: sendToGateway, initStreamListener,
@@ -343,7 +343,7 @@ export function ChatArea() {
         </div>
         <div className="flex items-center gap-4">
           {/* Token usage counter — DeerFlow-style plain text */}
-          {(totalInputTokens + totalOutputTokens) > 0 && (() => {
+          {!compact && (totalInputTokens + totalOutputTokens) > 0 && (() => {
             const total = totalInputTokens + totalOutputTokens;
             const display = total >= 1000 ? `${(total / 1000).toFixed(1)}K` : String(total);
             return (
@@ -353,7 +353,7 @@ export function ChatArea() {
             );
           })()}
           <OfflineIndicator compact />
-          {messages.length > 0 && (
+          {!compact && messages.length > 0 && (
             <Button
               variant="ghost"
               size="sm"
@@ -561,11 +561,12 @@ export function ChatArea() {
                 >
                   <Paperclip className="w-5 h-5" />
                 </Button>
-                <ChatMode
+                {!compact && <ChatMode
                   value={chatMode}
                   onChange={setChatMode}
                   disabled={isStreaming}
                 />
+                }
               </div>
               <div className="flex items-center gap-2">
                 <ModelSelector