feat(ClubSettings): add country and state code fields for regional calendar data

- Introduced `countryCode` and `stateCode` fields in the Club model to support regional calendar data.
- Updated ClubSettings component to allow users to select their country and state, enhancing the configuration options for clubs.
- Enhanced the ClubService to handle normalization of country and state codes during updates.
- Added new routes and middleware to support the training cancellation feature and calendar integration in the backend.
- Updated frontend navigation to include a calendar link, improving user access to scheduling features.

backend/migrations/add_calendar_region_to_clubs.sql

@@ -0,0 +1,3 @@
+ALTER TABLE clubs
+  ADD COLUMN IF NOT EXISTS country_code VARCHAR(2) NOT NULL DEFAULT 'DE',
+  ADD COLUMN IF NOT EXISTS state_code VARCHAR(16) NULL;

backend/migrations/add_range_to_training_cancellations.sql

@@ -0,0 +1,13 @@
+ALTER TABLE training_cancellations
+  ADD COLUMN IF NOT EXISTS start_date DATE NULL,
+  ADD COLUMN IF NOT EXISTS end_date DATE NULL;
+
+UPDATE training_cancellations
+SET
+  start_date = COALESCE(start_date, date),
+  end_date = COALESCE(end_date, date)
+WHERE start_date IS NULL OR end_date IS NULL;
+
+ALTER TABLE training_cancellations
+  MODIFY start_date DATE NOT NULL,
+  MODIFY end_date DATE NOT NULL;

backend/migrations/create_training_cancellations_table.sql

@@ -0,0 +1,14 @@
+CREATE TABLE IF NOT EXISTS training_cancellations (
+  id INT AUTO_INCREMENT PRIMARY KEY,
+  club_id INT NOT NULL,
+  start_date DATE NOT NULL,
+  end_date DATE NOT NULL,
+  date DATE NULL,
+  reason VARCHAR(255) NULL,
+  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  UNIQUE KEY uniq_training_cancellation_club_range (club_id, start_date, end_date),
+  CONSTRAINT fk_training_cancellations_club
+    FOREIGN KEY (club_id) REFERENCES clubs(id)
+    ON DELETE CASCADE
+);