fix: qwen hook failback fail closed

[josstei]

Summary

• Make the shared hook runner exit with deny semantics when adapter errors hit the fallback path.
• Update the Qwen adapter to emit a blocking fallback response instead of allowing execution through.
• Regenerate detached runtime surfaces and align Qwen docs with the current hook/output contract.
• Add unit and integration coverage for the Qwen invalid-stdin fallback path.

Testing

• npm run generate
• node --test tests/unit/platform-adapters.test.js tests/integration/hook-entrypoints.test.js
• npm test