v2.8.2 — server-level instructions (orient before the first guess)

Adds a server-level MCP instructions block — the first thing the model reads on initialize, before any tool call. Frames GA4-not-UA (training predates the live schema), tells the model not to hand-type field names (discover via search_schema, the only source of truth for the property), and routes interpretation to search_skills. Prevention at the top of the funnel; specifics stay in search_schema and the raw-fetch skills library.