feat!: prefix every tool with shopify_, and stay up when unconfigured

BREAKING: list_products is now shopify_list_products, and so on for all 13.
MCP servers share one flat tool namespace, and the unprefixed names collided
with other servers in this fleet — get_quote and cancel_order each existed in
three repos, and whichever loaded last silently won.

loadConfig also threw when credentials were missing, which surfaces as
'Connection closed' with the explanation swallowed; shopify_auth_status now
reports what to set.

Toolchain bumped to canon; LICENSE, .env.*, release script, stdio smoke test.