feat(tournaments): add partnership tracking and tournament management

Implement comprehensive partnership tracking system and tournament
management features including round-robin, single/double elimination,
and Swiss system pairings.

Changes:
- Add partnership_games and partnership_stats tables
- Implement PartnershipTracker service for recording partnership data
- Add tournament generator with multiple formats
- Create tournament management actions and views
- Add acceptance tests for partnership tracking
- Fix PartnershipTracker to use single snapshot per player per match
- Fix round-robin test to query by round_number instead of hardcoded ID

Note: All 8 acceptance tests now passing

app/templates/admin/tournaments/index.html.erb

@@ -0,0 +1,64 @@
+<h1>Tournament Administration</h1>
+
+<p><a href="/admin/tournaments/new">Create New Tournament</a></p>
+
+<% if upcoming.any? %>
+  <h2>Upcoming / Active Tournaments</h2>
+  <table>
+    <thead>
+      <tr>
+        <th>Name</th>
+        <th>Date</th>
+        <th>Format</th>
+        <th>Status</th>
+        <th>Actions</th>
+      </tr>
+    </thead>
+    <tbody>
+      <% upcoming.each do |tournament| %>
+        <tr>
+          <td><%= tournament.name %></td>
+          <td><%= tournament.event_date&.strftime('%Y-%m-%d %H:%M') %></td>
+          <td><%= tournament.format %></td>
+          <td><%= tournament.status %></td>
+          <td>
+            <a href="/admin/tournaments/<%= tournament.id %>">View</a> |
+            <a href="/admin/tournaments/<%= tournament.id %>/edit">Edit</a>
+          </td>
+        </tr>
+      <% end %>
+    </tbody>
+  </table>
+<% end %>
+
+<% if completed.any? %>
+  <h2>Past Tournaments</h2>
+  <table>
+    <thead>
+      <tr>
+        <th>Name</th>
+        <th>Date</th>
+        <th>Format</th>
+        <th>Actions</th>
+      </tr>
+    </thead>
+    <tbody>
+      <% completed.each do |tournament| %>
+        <tr>
+          <td><%= tournament.name %></td>
+          <td><%= tournament.event_date&.strftime('%Y-%m-%d') %></td>
+          <td><%= tournament.format %></td>
+          <td>
+            <a href="/admin/tournaments/<%= tournament.id %>">View Results</a>
+          </td>
+        </tr>
+      <% end %>
+    </tbody>
+  </table>
+<% end %>
+
+<% if upcoming.empty? && completed.empty? %>
+  <p>No tournaments yet. <a href="/admin/tournaments/new">Create your first tournament!</a></p>
+<% end %>
+
+<p><a href="/admin/players">Back to Admin</a></p>