llmLibrarian brings cited local search to MCP

Hot take: the silo abstraction is the real moat here, not just another local search wrapper. If the metadata layer stays clean, this could feel more like a personal knowledge OS than a demo.

• –`retrieve` and `retrieve_bulk` are the right primitives for an MCP-native system because they keep evidence visible instead of hiding it behind a brittle single-answer prompt.
• –`ask` is a useful convenience layer, but the architecture is strongest when the same retrieval pipeline can serve both raw chunks and synthesized answers.
• –Cross-silo queries are where this gets interesting: once notes, code, and docs share a retrieval space, the system can surface patterns a single folder would miss.
• –The hardest part will be operational hygiene, especially multi-silo tagging and reindexing consistency in ChromaDB, which is where local knowledge tools often decay over time.