Add price prediction feature to dashboard

Enter a hypothetical BTC price to instantly see predicted portfolio value,
predicted P&L, and difference vs current value — all calculated client-side.

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

btc-portfolio/frontend/src/pages/Dashboard.js

@@ -17,6 +17,13 @@ const styles = {
   adminBtn: { background: 'none', border: '1px solid #f7931a', color: '#f7931a', borderRadius: '8px', padding: '0.4rem 1rem', cursor: 'pointer', textDecoration: 'none', fontSize: '1rem' },
   headerBtns: { display: 'flex', gap: '0.5rem', alignItems: 'center' },
   statsGrid: { display: 'grid', gridTemplateColumns: 'repeat(3, 1fr)', gap: '1rem', marginBottom: '1.5rem' },
+  predictionSection: { background: '#1a1a1a', border: '1px solid #333', borderRadius: '12px', padding: '1rem', marginBottom: '1.5rem' },
+  predictionHeader: { color: '#888', fontSize: '0.8rem', marginBottom: '0.75rem' },
+  predictionRow: { display: 'flex', gap: '1rem', alignItems: 'flex-start', flexWrap: 'wrap' },
+  predictionInputWrap: { display: 'flex', flexDirection: 'column', gap: '0.3rem' },
+  predictionLabel: { color: '#888', fontSize: '0.8rem' },
+  predictionInput: { background: '#111', border: '1px solid #444', borderRadius: '8px', color: '#fff', padding: '0.55rem 0.75rem', fontSize: '1rem', width: '160px', outline: 'none' },
+  predictionCards: { display: 'flex', gap: '1rem', flex: 1, flexWrap: 'wrap' },
   statCard: { background: '#1a1a1a', padding: '1rem', borderRadius: '12px', border: '1px solid #333' },
   statLabel: { color: '#888', fontSize: '0.8rem', marginBottom: '0.3rem' },
   statValue: { fontSize: '1.2rem', fontWeight: 700 },
@@ -53,6 +60,7 @@ export default function Dashboard() {
   const [candlesAll, setCandlesAll] = useState(null);
   const [fullscreenChart, setFullscreenChart] = useState(false);
   const [chartView, setChartView] = useState('both'); // 'both' | 'portfolio' | 'history'
+  const [predictionPrice, setPredictionPrice] = useState('');
   const navigate = useNavigate();
 
   const authHeaders = () => ({
@@ -107,6 +115,12 @@ export default function Dashboard() {
     setFullscreenChart(f => !f);
   }, [fullscreenChart, candlesAll, fetchAllCandles]);
 
+  const predPrice = parseFloat(predictionPrice);
+  const predValid = stats && predictionPrice !== '' && predPrice > 0;
+  const predValue = predValid ? +(stats.total_btc * predPrice).toFixed(2) : null;
+  const predPL = predValid ? +(predValue - stats.total_invested).toFixed(2) : null;
+  const predVsCurrent = predValid ? +(predValue - stats.portfolio_value).toFixed(2) : null;
+
   const plHighlight = stats
     ? stats.profit_loss >= 0 ? 'positive' : 'negative'
     : 'neutral';
@@ -143,6 +157,42 @@ export default function Dashboard() {
         </div>
       )}
 
+      <div style={styles.predictionSection}>
+        <div style={styles.predictionHeader}>Price Prediction</div>
+        <div style={styles.predictionRow}>
+          <div style={styles.predictionInputWrap}>
+            <label style={styles.predictionLabel}>BTC Price (€)</label>
+            <input
+              type="number"
+              min="0"
+              placeholder="e.g. 100000"
+              value={predictionPrice}
+              onChange={e => setPredictionPrice(e.target.value)}
+              style={styles.predictionInput}
+            />
+          </div>
+          {predValid && (
+            <div style={styles.predictionCards}>
+              <StatCard
+                label="Predicted Value"
+                value={`€${predValue.toLocaleString()}`}
+                highlight="neutral"
+              />
+              <StatCard
+                label="Predicted P&L"
+                value={`${predPL >= 0 ? '+' : ''}€${predPL.toLocaleString()}`}
+                highlight={predPL >= 0 ? 'positive' : 'negative'}
+              />
+              <StatCard
+                label="vs. Current"
+                value={`${predVsCurrent >= 0 ? '+' : ''}€${predVsCurrent.toLocaleString()}`}
+                highlight={predVsCurrent >= 0 ? 'positive' : 'negative'}
+              />
+            </div>
+          )}
+        </div>
+      </div>
+
       <div style={styles.tabs}>
         {[['both', 'Both'], ['portfolio', 'Portfolio'], ['history', 'BTC Candles']].map(([key, label]) => (
           <button