feat(kaisertisch): implement Kaisertisch tournament functionality with model, routes, and controller

backend/migrations/20260819_create_kaisertisch_tournaments.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS kaisertisch_tournaments (
+  id INT AUTO_INCREMENT PRIMARY KEY,
+  club_id INT NOT NULL,
+  diary_date_id INT NOT NULL,
+  state JSON NOT NULL,
+  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  UNIQUE KEY uniq_kaisertisch_tournament_club_date (club_id, diary_date_id),
+  CONSTRAINT fk_kaisertisch_tournament_club FOREIGN KEY (club_id) REFERENCES clubs(id) ON DELETE CASCADE,
+  CONSTRAINT fk_kaisertisch_tournament_date FOREIGN KEY (diary_date_id) REFERENCES diary_dates(id) ON DELETE CASCADE
+);