feat(hyperhdr): vendor the flatbuffers schemas and generated bindings

The .fbs files come from HyperHDR (see schema/NOTICE); the *_generated.rs
files are flatc output regenerated by scripts/regen-fbs.sh, which refuses to
run unless flatc matches the pinned flatbuffers crate.

schema/hyperhdr_reply.fbs

@@ -0,0 +1,13 @@
+// Copied verbatim from HyperHDR (https://github.com/awawa-dev/HyperHDR),
+// include/flatbuffers/parser/hyperhdr_reply.fbs @ 3a76dcd (24.0.0-beta.0).
+// Copyright (c) 2020-2026 awawa-dev. MIT License, see schema/NOTICE.
+
+namespace hyperhdrnet;
+
+table Reply {
+  error:string;
+  video:int = -1;
+  registered:int = -1;
+}
+
+root_type Reply;