Initial release of an Enterovirus A71 dataset

[nneune]

Enterovirus A71 dataset

This pull request introduces the initial release of a Nextclade dataset for Enterovirus A71 (EV-A71), designed for lineage classification, subgenotype assignment, mutation analysis, sequence quality control, and phylogenetic placement. The dataset uses a reconstructed ancestral sequence as the reference, which is genetically closer to currently circulating EV-A71 strains and supports more accurate analyses compared to historical prototypes.

The most important changes are:

Dataset Documentation and Metadata:

• Added a comprehensive README.md describing the dataset's scope, features, clade definitions, reference types, and usage guidance, including authorship and contact information.
• Added a CHANGELOG.md noting this as the initial release and providing a link to Nextclade dataset documentation.

Reference Data and Annotation:

• Added reference.fasta containing the inferred ancestral EV-A71 sequence, which serves as the main reference for mutation calling and sequence alignment.
• Added genome_annotation.gff3 with detailed genome feature annotations (e.g., CDS for VP4, VP2, VP3, VP1, and non-structural proteins) based on the BrCr prototype sequence.

Checklist

• Send to ENPEN for testing