AI Coach: 클라이언트 API 키 제거, 백엔드 프록시로 전환

- Anthropic API 직접 호출 → /api/stock/ai-coach 백엔드 프록시로 변경
- API 키 입력 UI 제거 (서버에서 관리)
- aiApiKey 상태 변수 및 localStorage 저장 로직 제거

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/pages/stock/StockTrade.jsx

@@ -232,8 +232,7 @@ const StockTrade = () => {
     const [reportSortDir, setReportSortDir] = useState('desc');
 
     /* AI Coach */
-    const [aiApiKey, setAiApiKey] = useState('');
-    const [aiModel, setAiModel] = useState('claude-haiku-4-5-20251001');
+    const [aiModel, setAiModel] = useState(() => localStorage.getItem('ai_coach_model') ?? 'claude-haiku-4-5-20251001');
     const [aiResult, setAiResult] = useState(null);
     const [aiLoading, setAiLoading] = useState(false);
     const [aiError, setAiError] = useState('');
@@ -377,12 +376,8 @@ const StockTrade = () => {
         }
     }, [activeTab, assetHistoryDays, loadAssetHistory]);
 
-    /* AI Coach: 마운트 시 localStorage에서 API Key + 오늘 캐시 복원 */
+    /* AI Coach: 마운트 시 오늘 캐시 복원 */
     useEffect(() => {
-        const savedKey = localStorage.getItem('ai_coach_key') ?? '';
-        const savedModel = localStorage.getItem('ai_coach_model') ?? 'claude-haiku-4-5-20251001';
-        setAiApiKey(savedKey);
-        setAiModel(savedModel);
         const today = new Date().toISOString().slice(0, 10);
         const cached = localStorage.getItem(`ai_coach_${today}`);
         if (cached) {
@@ -707,7 +702,7 @@ const StockTrade = () => {
     /* ── AI coach ────────────────────────────────────────────────── */
 
     const handleAiCoach = async () => {
-        if (!aiApiKey.trim() || portfolioHoldings.length === 0) return;
+        if (portfolioHoldings.length === 0) return;
 
         const today = new Date().toISOString().slice(0, 10);
         const cacheKey = `ai_coach_${today}`;
@@ -755,24 +750,15 @@ ${holdingsText}${marketText}
 }`;
 
         try {
-            const res = await fetch('https://api.anthropic.com/v1/messages', {
+            const res = await fetch('/api/stock/ai-coach', {
                 method: 'POST',
-                headers: {
-                    'Content-Type': 'application/json',
-                    'x-api-key': aiApiKey.trim(),
-                    'anthropic-version': '2023-06-01',
-                    'anthropic-dangerous-direct-browser-access': 'true',
-                },
-                body: JSON.stringify({
-                    model: aiModel,
-                    max_tokens: 1024,
-                    messages: [{ role: 'user', content: prompt }],
-                }),
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ model: aiModel, prompt, max_tokens: 1024 }),
             });
 
             if (!res.ok) {
-                const text = await res.text().catch(() => '');
-                throw new Error(`Claude API 오류 (${res.status}): ${text.slice(0, 200)}`);
+                const errData = await res.json().catch(() => ({}));
+                throw new Error(errData.error || `AI Coach 오류 (${res.status})`);
             }
 
             const data = await res.json();
@@ -2467,30 +2453,8 @@ ${cashLines}
                             </div>
                         )}
 
-                        {/* API Key 설정 */}
+                        {/* 모델 선택 */}
                         <div className="ai-coach-settings">
-                            <label>
-                                Anthropic API Key
-                                <div className="ai-coach-key-row">
-                                    <input
-                                        type="password"
-                                        className="ai-coach-key-input"
-                                        value={aiApiKey}
-                                        onChange={(e) => setAiApiKey(e.target.value)}
-                                        placeholder="sk-ant-api03-..."
-                                    />
-                                    <button
-                                        className="button ghost small"
-                                        type="button"
-                                        onClick={() => {
-                                            localStorage.setItem('ai_coach_key', aiApiKey);
-                                            localStorage.setItem('ai_coach_model', aiModel);
-                                        }}
-                                    >
-                                        저장
-                                    </button>
-                                </div>
-                            </label>
                             <label>
                                 AI 모델
                                 <select
@@ -2511,7 +2475,7 @@ ${cashLines}
                                 className="button primary"
                                 type="button"
                                 onClick={handleAiCoach}
-                                disabled={aiLoading || !aiApiKey.trim() || portfolioHoldings.length === 0}
+                                disabled={aiLoading || portfolioHoldings.length === 0}
                             >
                                 {aiLoading ? 'AI 분석 중...' : '오늘 투자 평가 받기'}
                             </button>