v0.3.0 — conversation store + ask()

Durable, resumable conversations across all five ports.

• ConversationStore provider (get(id) / save(id, messages)) with an in-memory default; set once on the client via create_client(..., store). Bring your own for file/db/redis.
• client.ask(prompt, { toolkit, id? }) — with id: loads that id's transcript, runs, saves it → the next ask with the same id continues the conversation. Without id: a stateless one-shot (= run). openai + anthropic.
• A2A serve remembers by contextId — served conversations persist through the same store.

Backward-compatible. npm i toolnexus · pip install toolnexus · go get github.com/muthuishere/toolnexus/golang@v0.3.0 · dotnet add package Toolnexus --version 0.3.0 · io.github.muthuishere:toolnexus:0.3.0