fix(embedding): cap remote batch size at 10

[YOMXXX]

Summary

• cap remote embedding batch size at 10 so Dashscope/Tencent-compatible APIs do not reject L0 background embedding batches
• keep existing chunking behavior for OpenAI-compatible and ZeroEntropy remote embedding services
• add a regression test that fails when 11 inputs are sent as one remote batch

Closes #236

Test plan

• npx vitest run src/core/store/embedding.test.ts
• npm test
• npm run build

Notes

• npm run test:cc-plugin -- --run currently fails because package.json has no test:cc-plugin script.

[Maxwell-Code07]

Awesome work! 13 fixes in one batch covering Gateway hardening, embedding compatibility, Hermes memory injection, offload stability, and pipeline optimization — a very productive cleanup session 👏

We'll review and merge them one by one 🚀