Add pluggable balance registry, OpenRouter credits/key limit client,
and llm-connect balance with one-shot --provider that does not change
library defaults.
Copy markitect.llm module into standalone llm_connect package.
All markitect.* imports replaced with llm_connect.* equivalents.
LLMError base class inlined (no markitect.exceptions dependency).
Verified: from llm_connect import create_adapter works.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>