ci: add OpenCode GitHub agent workflow

Simplify retry decorator and add builder dependency group

docs: add sync comments for EMBED_MODEL across builder, Dockerfile, workflow

fix: restore fetch-depth=0 for full clone required by HF push

refactor: simplify cleanup from /simplify review

ci: replace FastMCP redeploy with HF Spaces restart + sync workflow

migrate to Hugging Face Spaces; consolidate builder module

feat: resilient indexer with retry, limit, and incremental cache

feat: add xkcd semantic search MCP server with daily indexing