fix(stage-b): Add sh_core using + Stage-1 JSON support

## Fixed Issues

1. compiler_stageb.hako: Added 'using sh_core as StringHelpers'
   - Resolved: call unresolved ParserStringUtilsBox.skip_ws/2
   - Root cause: using chain resolution not implemented
   - Workaround: explicit using in parent file

2. stageb_helpers.sh: Accept Stage-1 JSON format
   - Modified awk pattern to accept both formats:
     - MIR JSON v0: "version":0, "kind":"Program"
     - Stage-1 JSON: "type":"Program"

## Remaining Issues

ParserBox VM crash: Invalid value: use of undefined value ValueId(5839)
- Cause: Complex nested loops in parse_program2()
- Workaround: Minimal Stage-B (without ParserBox) works
- Fallback: Rust compiler path available

## Verification

✅ Minimal Stage-B outputs JSON correctly
❌ ParserBox execution crashes VM (SSA bug)

Co-Authored-By: Task先生 (AI Agent)

apps/examples/json_query_min/main.nyash

@@ -89,3 +89,4 @@ static box Main {
     return null
   }
 }
+}