Add allowlist of backup file extensions (sql, sql.gz, tar, tgz, zip,
dump, bak, bson, archive, bz2, xz, and compound variants) and enforce
a 10 GiB maximum file size on the backup upload endpoint. Validation
runs early on each chunk using the dropzone metadata and again on the
assembled file. Also drops the unused createFilename helper and the
commented-out S3 block.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
