json: add v2 JsonDoc/JsonNode plugin with runtime provider switch; vendored yyjson + FFI; loader resolve(name)->method_id; PyVM JSON shims; smokes + CI gate; disable MiniVmPrints fallbacks by default

- plugin_loader_v2: store per-Box resolve() from TypeBox FFI; add resolve_method_id() and use in invoke_instance_method
- plugin_loader_unified: resolve_method() falls back to loader’s resolve when TOML lacks method entries
- nyash.toml: register JsonDocBox/JsonNodeBox methods (birth/parse/root/error; kind/get/size/at/str/int/bool)
- plugins/nyash-json-plugin:
  * serde/yyjson provider switch via env NYASH_JSON_PROVIDER (default serde)
  * vendored yyjson (c/yyjson) + shim; parse/root/get/size/at/str/int/bool implemented for yyjson
  * TLV void returns aligned to tag=9
- PyVM: add minimal JsonDocBox/JsonNodeBox shims in ops_box.py (for dev path)
- tests/smokes: add jsonbox_{parse_ok,parse_err,nested,collect_prints}; wire two into min-gate CI
- tools: collect_prints_mixed now uses JSON-based app
- MiniVmPrints: move BinaryOp and fallback heuristics behind a dev toggle (default OFF)
- CURRENT_TASK.md: updated with provider policy and fallback stance

.github/workflows/min-gate.yml

@@ -45,6 +45,12 @@ jobs:
       - name: Run PyVM Stage-2 smokes
         run: bash tools/pyvm_stage2_smoke.sh
 
+      - name: JSON smoke — collect_prints (PyVM+plugins)
+        run: bash tools/test/smoke/selfhost/jsonbox_collect_prints.sh
+
+      - name: JSON smoke — parse error (PyVM+plugins)
+        run: bash tools/test/smoke/selfhost/jsonbox_parse_err.sh
+
   macro-golden:
     runs-on: ubuntu-latest
     timeout-minutes: 20