fix: lobby creation 500 — P2002 not caught when meta.target is null (Prisma 7)

[KovalDenys1]

Bug

Creating a lobby sometimes throws a 500 error instead of retrying with a new code:

Invalid `prisma.lobbies.create()` invocation
Unique constraint failed on the fields: (`code`)

Root Cause

isLobbyCodeConflict() in app/api/lobby/route.ts checks meta.target to confirm the P2002 is for the code field. In Prisma 7, meta.target can be null/undefined even on a genuine code collision, causing the function to return false and the API to throw instead of retry.

Fix

Add fallback: when prismaCode === 'P2002' and target is absent, check the error message string for "unique constraint"" + "code"; if that also fails, return true (any P2002 on lobbies.create must be the code field).