Backend invoke bridge for Flutter Adaptive Cards — request serialization, response parsing, and handler wiring. Changelog excerpt: ### Security 0.12.0 - **Bounded backend response decoding:** `HttpAdaptiveCardBackendClient`gains `maxResponseBytes`(default 1 MiB) and decodes via `decodeJsonMapWithLimit`, throwing `AdaptiveJsonTooLargeException`on oversized bodies instead of decoding unbounded untrusted JSON. - **Optional `replaceCard`validator:** `AdaptiveCardInvokeResponse.applyTo`and `AdaptiveCardBackendHandlers.wrap`accept an `AdaptiveCardValidator`; a backend-supplied replacement card that fails validation is rejected ([...]