fix(openclaw): gate append retention on stored text

[xmh1011]

Summary

• parse /version feature flags in the OpenClaw append capability probe
• require both API version >= 0.5.0 and features.store_document_text=true before sending update_mode=append
• fall back to per-turn document IDs when document text storage is disabled
• add regression coverage for legacy payloads, enabled text storage, disabled text storage, and older API versions

Tests

• npm test -- src/index.test.ts
• npm run build
• ./scripts/hooks/lint.sh

Closes #2505

[koriyoshi2041]

I had a duplicate patch open for this path and closed it in favor of this one.

I compared this against #2505 and the current /version surface: FeaturesInfo exposes store_document_text as an explicit bool, and tests/test_store_document_text.py covers the disabled response. The stricter helper here, where append requires stored document text, matches that contract.

Local third-party check on this head:

cd hindsight-integrations/openclaw
npm test
# Test Files  9 passed (9)
# Tests       281 passed (281)