feat(types): dropin/headless doc sync for June '26

[cdevos-purse]

Summary

Consolidates #88 and #89 — both bot PRs were byte-for-byte identical (same generated output), so this replaces them with a single clean commit.

Targets v0.9.0 (minor bump driven by feat: squash commit on merge).

New API surface

Wallet / tokens

• WalletAPI.setAsFavorite({ id }) — mark a token as favorite via the wallet API
• PurseHeadlessCheckoutPrimaryToken.isFavorite — reactive Readable<boolean>
• PurseHeadlessCheckoutPrimaryToken.setAsFavorite() — convenience wrapper
• PurseHeadlessCheckoutToken.createdAt? — ISO 8601 creation date for chronological sorting
• IntegratedToken.created_at? — raw wallet field

Hosted fields

• PurseHeadlessCheckoutPrimaryMethod.supportsHostedFields — whether method supports iframe card input
• PurseHeadlessCheckoutPrimaryToken.supportsHostedFields — same on token level
• PurseHeadlessCheckoutGetPaymentElementOptions.partner made optional (match by method alone)
• PurseHeadlessCheckoutGetPaymentElementOptions.xPayButton? — Apple Pay / Google Pay button config
• New error METHOD_DOES_NOT_SUPPORT_HOSTED_FIELDS (replaces silent warning)

Dropin theme

• DropinTheme.title.color? — title text color override
• DropinTheme.xpay? — Apple Pay (buttonstyle) + Google Pay (buttonColor) theme controls

Session

• PaymentSession.source narrowed to LegacyPaymentSession; rawSource? holds the OrchestrationPaymentSession
• Payment.setSession / PursePayment.setSession signature narrowed accordingly

i18n

• common.sessionExpiredTitle, common.sessionExpiredBody, common.refreshPageToTryAgain added across all locales

Dropin hooks

• InitOptions.hooks.onRefreshSession return type broadened to PurseHeadlessCheckoutV1Params["paymentSession"] | string | void

Test plan

• CI build + lint + check-exports + unit tests pass on this PR
• After merge: on-push-main release workflow creates tag v0.9.0, bumps package.json, updates CHANGELOG.md