Set up automatic icp CLI upgrades

A one-time installer: it adds a SessionStart hook that checks whether icp and ic-wasm are current and — if the user wants — upgrades them before work starts. Once these steps are done the user never needs this skill again.

ic-wasm is covered alongside icp because the official recipes (@dfinity/motoko, @dfinity/rust, @dfinity/static-site, @dfinity/asset-canister) invoke it on every build. An ic-wasm left behind while icp moves forward produces build failures that read as recipe bugs, so upgrading only one of the pair is the worse default.

icp has its own check (icp settings update-check) that is worth leaving on, but it only speaks once the user runs an icp command — by which point the agent has already chosen what to write. This hook runs before the session's first prompt, so the version reaches Claude's context up front, and it covers ic-wasm too.

Step 1 — Ask the user which mode they want

The installer cannot make this call for the user, so ask before writing anything: