Phase 21.6 solidification: chain green (return/binop/loop/call); add Phase 21.7 normalization plan (methodize static boxes). Update CURRENT_TASK.md and docs.

src/runner/json_v0_bridge/lexer.rs

@@ -185,6 +185,7 @@ pub(super) fn parse_source_v0_to_json(input: &str) -> Result<String, String> {
         version: 0,
         kind: "Program".into(),
         body: vec![StmtV0::Return { expr }],
+        defs: vec![],
     };
     serde_json::to_string(&prog).map_err(|e| e.to_string())
 }