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/repositories/event_participants.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+require 'rom-repository'
+
+module EuchreCamp
+  module Repositories
+    class EventParticipants < ::EuchreCamp::Repository[:event_participants]
+      commands :create, update: :by_pk, delete: :by_pk
+
+      def by_event(event_id)
+        event_participants.where(event_id: event_id).to_a
+      end
+
+      def players_by_event(event_id)
+        # Return player IDs registered for an event
+        event_participants
+          .where(event_id: event_id)
+          .select(:player_id)
+          .to_a
+          .map { |p| p[:player_id] }
+      end
+
+      def register_player(event_id, player_id, seed: nil)
+        create(
+          event_id: event_id,
+          player_id: player_id,
+          status: 'registered',
+          seed: seed
+        )
+      end
+
+      def remove_player(event_id, player_id)
+        event_participants
+          .where(event_id: event_id, player_id: player_id)
+          .delete
+      end
+    end
+  end
+end