Add an MCP prompt for post-cook archive summaries

[jongio]

The MCP server exposes cook data and several action tools, but an assistant still has to piece together a post-cook summary by hand.

Acceptance criteria:

• Add one MCP prompt for summarizing a finished archive.
• The prompt instructs the assistant to call existing archive and history tools.
• The output asks for timings, temp swings, alarms, and next-cook notes.
• No new API surface is needed beyond the prompt.

[jongio]

Research refresh: cook history, annotations, and repeatable post-cook learning remain a common gap across BBQ monitoring apps. This fits the MCP server because the archive and history tools already expose the needed data, so a prompt can guide the assistant without adding a new API.

Implementation note: add a prompt that asks the assistant to call archive search or detail, pull temperature history when needed, and return timings, temp swings, alarms, and next-cook notes.