fuzz-target-payload-codec: the §3.1 target — all five invariants in shared, thin fuzz_target wrapper, 97 committed seeds + gitignore negation + README row; placeholder bin replaced; serde (derive) added to shared

fuzz/fuzz_targets/payload_codec.rs

@@ -0,0 +1,10 @@
+//! The §3.1 target: core's payload encode/decode invariants, driven
+//! through the already-`pub` `encode_payload` / `payload_as` surface.
+
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    alkstore_fuzz_shared::payload_codec::fuzz_payload_codec(data);
+});