feat: implement WASM phase 1 DValue ABI

site/doc/pages/ucb_encode.txt

@@ -0,0 +1,23 @@
+:title
+ucb_encode
+
+:sig
+String ucb_encode(DValue value)
+
+:see
+ucb_decode
+0_DValue
+json_encode
+
+:content
+Serializes a `DValue` to UCEB1, UCE's binary DValue wire format for the WASM membrane and future cross-instance calls.
+
+UCEB1 is length-prefixed and binary-safe. It preserves nested maps, list-shaped maps, empty lists, and scalar bytes, including embedded NUL bytes. Use JSON/YAML/XML serializers for human-facing formats; use UCEB1 when UCE code needs the native DValue protocol.
+
+```cpp
+DValue payload;
+payload["name"] = "uce";
+payload["items"].push("first");
+
+String bytes = ucb_encode(payload);
+```