src/lib/llmClient.ts: browser POSTs to /internal/canvas-llm/chat with
{messages, max_tokens}. Mirrors the normalized request shape used by
earendil-works/pi's @earendil-works/pi-ai. Returns:
- ok:true with content+provider when configured and successful
- ok:false, configured:false when proxy 404/503/unreachable
- ok:false, configured:true when provider returned an error
routeAgentInput now falls back to the LLM with a system prompt that
includes the user identity, tool catalogue, and the top-3 vault recall
hits when no deterministic tool matches. When the proxy is not
configured the deterministic vault-hint reply is used (no regression
in the demo tier).
