Add bulk /users/full lookup

[cmyui]

Summary

• keep /api/v1/users/full?id=... returning the existing single-user object
• add /api/v1/users/full?ids=1&ids=2... returning { code, users } with a hard 50-id limit
• batch full-user SQL reads for stats, followers, badges, tournament badges, and clans
• add country_name to full user responses and reuse the existing country list

Verification

• CGO_ENABLED=0 go test ./app/v1
• CGO_ENABLED=0 go test ./... still fails on existing common/where_test.go type mismatch for WhereClause.In