PERF: JMAP batch operations execute sequentially instead of using native batching

[andrinoff]

Is your feature request related to a problem?

In backend/jmap/jmap.go (lines 369-396), batch operations (DeleteEmails, ArchiveEmails, MoveEmails) loop through UIDs one-by-one:

for _, uid := range uids {
    if err := p.DeleteEmail(ctx, folder, uid); err != nil {
        return err
    }
}

JMAP supports multiple method invocations in a single request (RFC 8620 Section 3.3) but the code doesn't use this.

Describe the solution you'd like

Build a single JMAP request with all operations batched. Handle partial failure with proper error aggregation. Implement transaction rollback on batch failure.

[floatpanebot]

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[floatpanebot]

Closing due to inactivity. Reopen if still relevant.