Implement official PDGA rating calculation methodology

- Update predicted rating algorithm to match PDGA rating guide
- Focus on tournaments from last 12 months only (improved accuracy)
- Add proper outlier exclusion: rounds >2.5 std dev below average
- Implement double weighting for most recent 25% of rounds (9+ rounds)
- Apply PDGA minimum data requirements (7 rounds for outlier exclusion)
- Improve error handling and rate limiting for tournament scraping
- Add user-friendly error messages for failed calculations
- Reduce tournament scraping from 15 to 8 tournaments to avoid rate limits

🤖 Generated with [Claude Code](https://claude.ai/code)

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

index.html

@@ -315,7 +315,7 @@
                 
                 const data = await response.json();
                 
-                if (data.predictedRating) {
+                if (data.predictedRating && data.predictedRating > 0) {
                     predictedCell.textContent = data.predictedRating;
                     
                     const currentRating = parseInt(document.querySelector(`#row-${pdgaNumber} .rating`).textContent);
@@ -326,8 +326,8 @@
                     diffCell.className = `difference ${diffClass}`;
                     diffCell.textContent = diffText;
                 } else {
-                    predictedCell.textContent = 'Error';
-                    diffCell.textContent = 'Error';
+                    predictedCell.textContent = 'N/A';
+                    diffCell.innerHTML = '<span style="color: #999; font-size: 12px;">Unable to calculate<br>(Try again later)</span>';
                 }
                 
             } catch (error) {