fix(social): Make CreateFriendship idempotent

[seer-by-sentry]

This PR addresses the Microsoft.EntityFrameworkCore.DbUpdateException occurring when CreateFriendship is called multiple times for the same user pair, leading to a duplicate primary key violation in the Friends table.

The root cause was that CreateFriendship unconditionally attempted to insert a new FriendEntry without first checking for its existence. This could happen due to race conditions or repeated client requests.

The solution implements a two-layer defense:

1. An AnyAsync() check is added before insertion to prevent adding duplicate entries in most cases.
2. The catch block is enhanced to specifically handle MySqlConnector.MySqlException with error code 1062 (ER_DUP_ENTRY). This ensures that if a race condition still leads to a duplicate insert attempt, the exception is silently ignored, as the desired state (friendship exists) has already been achieved by a concurrent operation.

This makes the CreateFriendship method idempotent and prevents the DbUpdateException.

Fixes SERVICES-3W