Migrate @waniwani/sdk 0.17 → 0.18

A self-contained migration for the single hop from 0.17.x to 0.18.0. Apply it when a project on 0.17 is moving to 0.18. It covers only that jump; for other version boundaries use the matching migrate-waniwani-sdk-<from>-to-<to> skill, or the general procedure in the SDK's changelog.

Precondition: the project is on @waniwani/sdk@0.17.x. If it is on an older version, migrate up to 0.17 first (each jump ships its own migration skill); if it is already on 0.18+, there is nothing to do here.

What 0.18 changes

The generic funnel events quote.requested, quote.succeeded, quote.failed, and purchase.completed are removed from EVENT_TYPES and the TrackEvent union. They predate the typed revenue taxonomy (price_shown, prices_compared, option_selected, lead_qualified, converted), which models the same funnel stages with typed properties and flat track.* helpers.

Removed with them:

• The type exports QuoteSucceededProperties and PurchaseCompletedProperties (from @waniwani/sdk and @waniwani/sdk/mcp's tracking surface)
• The legacy input fields quoteAmount, quoteCurrency, purchaseAmount, purchaseCurrency on LegacyTrackEvent

Not affected: link.clicked (and LinkClickedProperties, legacy linkUrl) stays a first-class event, on both track() and the chat widget's separate host-page onEvent channel.

Unlike the 0.17 hop, this break is visible to tsc: every removed event name and type import surfaces as a type error after the bump, so the compiler output is the complete call-site list.