feat(MembersOverview): add season filter and enhance age group selection

- Introduced a new season filter dropdown in the MembersOverviewSection for selecting the season start year.
- Enhanced age group selection by organizing options into groups for better clarity and added new age categories.
- Updated localization files to include new terms related to the season filter and age classifications across multiple languages.
- Improved the overall layout and styling of the filter components for a better user experience.

backend/migrations/20260401_add_adult_release_reserve_approved_to_member.sql

@@ -0,0 +1,10 @@
+-- Jugend-Freigaben (Schema wie backend/models/Member.js)
+-- Fehlende Spalten verursachen SequelizeDatabaseError ER_BAD_FIELD_ERROR bei getClubMembers.
+
+ALTER TABLE `member`
+  ADD COLUMN `adult_release_approved` TINYINT(1) NOT NULL DEFAULT 0
+    COMMENT 'Jugendspieler mit Freigabe fuer Erwachsene'
+    AFTER `member_form_handed_over`,
+  ADD COLUMN `adult_reserve_approved` TINYINT(1) NOT NULL DEFAULT 0
+    COMMENT 'Jugendspieler als Ersatz bei Erwachsenen zugelassen'
+    AFTER `adult_release_approved`;