Excessive memory allocation during VP8L decoding, reachable from
app/store/image/image.go:333 where image.Decode runs on uploaded data.
The existing DecodeConfig dimension guard doesn't cover it, since the
over-allocation happens during decode rather than from declared dimensions.
Tidies backend/_example/memory_store in the same commit: it carries the
backend's deps as indirect entries and would otherwise fail the example CI step.