Add Elo rating system with match entry and CSV upload

- Implement EloCalculator service for 2v2 Euchre matches
- Create background job processing with GoodJob
- Add single match entry form
- Add CSV upload for batch match entry
- Create player rankings view
- Add database schema for matches and elo snapshots

app/templates/admin/matches/upload.html.erb

@@ -0,0 +1,26 @@
+<h1>Upload Matches (CSV)</h1>
+
+<p>Upload a CSV file with the following columns:</p>
+<pre>
+played_at, team_1_p1_name, team_1_p2_name, team_1_score, team_2_p1_name, team_2_p2_name, team_2_score
+</pre>
+
+<form action="/admin/matches/process_upload" method="post" enctype="multipart/form-data">
+  <input type="hidden" name="_csrf_token" value="<%= csrf_token %>">
+  
+  <div>
+    <label for="csv_file">CSV File:</label>
+    <input type="file" id="csv_file" name="csv_file" accept=".csv" required>
+  </div>
+
+  <button type="submit">Upload</button>
+</form>
+
+<p><a href="/admin/matches">Back to Matches</a></p>
+
+<h2>Example CSV:</h2>
+<pre>
+played_at,team_1_p1_name,team_1_p2_name,team_1_score,team_2_p1_name,team_2_p2_name,team_2_score
+2026-03-26 10:00,Alice,Bob,10,Charlie,David,7
+2026-03-26 10:30,Alice,Bob,10,Charlie,David,7
+</pre>