[Protocol/Swift] Add support for ec_auth / ec_color_scheme

[markmur]

The Embedded Checkout Protocol spec defines ec_auth and ec_color_scheme query parameters alongside ec_version and ec_delegate, but the protocol layer only emitted the latter two.

Changes

• Emit ec_auth and ec_color_scheme query parameters from EmbeddedCheckoutProtocol.url.
• Replace the url(for:delegations:) arguments with an Options struct (delegations, colorScheme, auth) so the signature stays stable as the spec adds handshake parameters.
• Add a generated Delegation type sourced from the spec's x-delegations — string-backed and ExpressibleByStringLiteral, so known values are type-safe and unknown values round-trip. defaultDelegations now uses it.
• Keep ec_color_scheme a plain String at the protocol boundary; the kit owns the curated color-scheme set.
• Regenerate the public Swift API baseline.

[github-actions]

React Native — Coverage Report

Lines	Statements	Branches	Functions
	91.66% (319/348)	87.86% (181/206)	100% (82/82)

[github-actions]

Package Size

Platform	Artifact	Base	Head	Delta
Android	release AAR	613.4 KiB	613.4 KiB	0 B

Measured from the PR base SHA and PR head SHA. This comment reports package artifact sizes only; it is not a final app binary-size report.