fix: offer refresh button when round history is empty

When a player has rating_history (graph) but no round_history (per-round
detail), calculating a target produced a dead-end error. Now the modal
detects the NO_ROUNDS case and shows a button that triggers the existing
refresh-round-history endpoint and re-runs the calculation on success.
Handles the 24h rate-limit and other refresh errors explicitly.

public/css/players.css

@@ -353,3 +353,10 @@
 .target-rating-result .loading {
     color: var(--text-muted);
 }
+
+.target-rating-result .no-history-prompt {
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+    align-items: flex-start;
+}

public/js/players.js

@@ -615,6 +615,10 @@ async function calculateTargetRating(event) {
         clearResult();
 
         if (!response.ok || !data.success) {
+            if (response.status === 404 && data.errorType === 'NO_ROUNDS') {
+                renderNoHistoryPrompt(pdgaNumber, result);
+                return;
+            }
             const msg = data.details ? data.error + ': ' + data.details : (data.error || 'Calculation failed');
             _targetResultMsg(result, 'error', msg);
             return;
@@ -661,3 +665,61 @@ async function calculateTargetRating(event) {
 function closeTargetRatingModal(event) {
     document.getElementById('target-rating-modal').style.display = 'none';
 }
+
+function renderNoHistoryPrompt(pdgaNumber, container) {
+    const wrapper = document.createElement('div');
+    wrapper.className = 'no-history-prompt';
+
+    const msg = document.createElement('div');
+    msg.textContent = 'No round-level history is stored for this player yet. Refresh from PDGA to enable the calculation.';
+    wrapper.appendChild(msg);
+
+    const btn = document.createElement('button');
+    btn.type = 'button';
+    btn.className = 'btn btn-confirm';
+    btn.textContent = 'Refresh round history & calculate';
+    btn.addEventListener('click', function () { refreshHistoryThenCalculate(pdgaNumber); });
+    wrapper.appendChild(btn);
+
+    container.appendChild(wrapper);
+}
+
+async function refreshHistoryThenCalculate(pdgaNumber) {
+    const result = document.getElementById('target-rating-result');
+    while (result.firstChild) result.removeChild(result.firstChild);
+    _targetResultMsg(result, 'loading', 'Refreshing round history from PDGA — this may take up to 30 seconds...');
+
+    try {
+        const response = await fetch('/api/refresh-round-history/' + pdgaNumber, { method: 'POST' });
+        const data = await response.json();
+        while (result.firstChild) result.removeChild(result.firstChild);
+
+        if (response.status === 429) {
+            const hours = data.hoursRemaining ? data.hoursRemaining + ' hour(s)' : 'a while';
+            _targetResultMsg(result, 'error', 'Round history was refreshed recently. Try again in ' + hours + '.');
+            return;
+        }
+
+        if (!response.ok || !data.success) {
+            const msg = data.details ? data.error + ': ' + data.details : (data.error || 'Refresh failed');
+            _targetResultMsg(result, 'error', msg);
+            return;
+        }
+
+        if (data.debugLog) cachedDebugInfo[pdgaNumber] = data.debugLog;
+        const predictedCell = document.getElementById('predicted-' + pdgaNumber);
+        if (predictedCell) {
+            const predictedValue = predictedCell.querySelector('.predicted-value');
+            if (predictedValue) {
+                predictedValue.textContent = data.predictedRating || 'N/A';
+                predictedValue.dataset.stddev = data.stdDev || '';
+            }
+        }
+
+        await calculateTargetRating(null);
+    } catch (err) {
+        console.error('Error refreshing round history:', err);
+        while (result.firstChild) result.removeChild(result.firstChild);
+        _targetResultMsg(result, 'error', 'Network error during refresh. Please try again.');
+    }
+}