docs: document the prorated refund preference

[eandreeva-twr]

Refund Saver can now ask Apple to refund only the part of a purchase the user hasn't consumed yet, instead of the all-or-nothing choice between declining and granting.

Changes

refund-saver.mdx

• New Grant prorated refund row in the default-preference table, in the position the option occupies in the Dashboard.
• A paragraph on when to pick it — you keep the revenue for the consumed part instead of risking the whole payment on a decline.
• New section on how the consumed share is determined: Apple calculates it for auto-renewable subscriptions; for every other product type Adapty calculates it, from the virtual currency the purchase granted or from the elapsed access period. A fully consumed purchase goes out as a decline, an untouched one as a full refund, and a purchase with no usage signal carries no preference at all.
• Heading renamed from "Set a default refund behavior" to "Set a default refund preference". The Dashboard's Learn more link targets that anchor and currently lands on the page top; the rename fixes it. Nothing in the docs links to the old anchor.

adapty-api.yaml

• grant_prorated added to the three custom_preference enums and to the request-schema description.

Zone brief (apple-platform)

• Three dated notes: the Dashboard hard-codes docs anchors, so a heading rename in this area can break an in-product link that the link checker cannot see; the app-level and per-profile preferences are separate enums with different spellings; and no SDK exposes the prorated value.

Notes

The SDK snippets are deliberately untouched — every SDK still exposes only no_preference, grant, and decline, so the option reaches users through the Dashboard and the server-side API alone.

The Dashboard change adding this option had not shipped to production at the time of writing.

Verification

check-mdx-parse and lint-mdx pass, the spec parses with all three enums reading grant, grant_prorated, no_preference, decline, and check-links-diff reports 0 broken and 0 stale links.