138 bare db.Exec calls across 22 handler files silently dropped write
errors. Each is now wrapped with error check and zap logging.
4 QueryRow sites that legitimately return sql.ErrNoRows during normal
operation (new player mezfes, festa rankings, empty guild item box)
now filter it out to reduce log noise.
Fix unchecked error returns on bf.Seek(), db.Exec(), QueryRow().Scan(),
pkt.Build(), logger.Sync(), and binary.Write() calls. The linter now
passes with 0 errors, build compiles, and all tests pass with -race.
