refactor(clubSettings): remove myTischtennis club ID and update related logic

- Removed the myTischtennis club ID field from club settings and related backend logic.
- Updated the database migration to eliminate the my_tischtennis_club_id column.
- Adjusted frontend components and services to reflect the removal of the club ID, ensuring the use of association member number instead.
- Enhanced user interface hints to clarify the use of association member number for rankings.

backend/services/clubService.js

@@ -70,7 +70,6 @@ class ClubService {
     async updateClubSettings(userToken, clubId, {
         greetingText,
         associationMemberNumber,
-        myTischtennisClubId,
         myTischtennisFedNickname,
         autoFetchRankings
     }) {
@@ -80,7 +79,6 @@ class ClubService {
             throw new Error('clubnotfound');
         }
         const updates = { greetingText, associationMemberNumber };
-        if (myTischtennisClubId !== undefined) updates.myTischtennisClubId = myTischtennisClubId || null;
         if (myTischtennisFedNickname !== undefined) updates.myTischtennisFedNickname = myTischtennisFedNickname || null;
         if (autoFetchRankings !== undefined) updates.autoFetchRankings = !!autoFetchRankings;
         return await club.update(updates);

backend/services/memberService.js

@@ -396,14 +396,14 @@ class MemberService {
                 };
             }
 
-            const effectiveClubId = (club.myTischtennisClubId || '').trim() || account.clubId;
+            const effectiveClubId = (club.associationMemberNumber || '').trim() || account.clubId;
             const effectiveFedNickname = (club.myTischtennisFedNickname || '').trim() || account.fedNickname;
 
             if (!effectiveClubId || !effectiveFedNickname) {
                 console.error('[updateRatingsFromMyTischtennis] - Missing clubId or fedNickname:', {
                     clubId: effectiveClubId,
                     fedNickname: effectiveFedNickname,
-                    fromClub: !!(club.myTischtennisClubId && club.myTischtennisFedNickname)
+                    fromClub: !!(club.associationMemberNumber && club.myTischtennisFedNickname)
                 });
                 return {
                     status: 400,