feat: Add UI layer (screens, components, views)

[bthebladeprimer]

Summary

• Add 20+ SwiftUI screens: card form, payment method selection, ACH (mandate, user details, bank collector), Apple Pay, Klarna, PayPal, QR Code, web/form redirect, vaulted payment methods list, country selection, success, error, loading, splash, and delete confirmation
• Add reusable UI components: input fields (card number, CVV, expiry, cardholder name, email, address, city, state, postal code, OTP), card network selectors (inline + dropdown), payment method buttons/sections, vault section, Apple Pay button
• Add infrastructure: PrimerInputFieldContainer system with styling/rendering extensions, SecureTextField, PrimerTextFieldExtension
• Add design system: CheckoutColors, PrimerLayout, AnimationConstants, SlideInModifier
• Add PrimerSwiftUIBridgeViewController for UIKit integration
• Add preview utilities: MockCardFormScope, MockDIContainer, MockDesignTokens, MockValidationService
• Add RTL support utilities

Context

PR 14 of 16 in the CheckoutComponents feature split. Depends on PR 13 (presentation scopes & container wiring).

Notion tracker

Test plan

• Visual review of SwiftUI screens via Xcode previews
• Verify input field components render correctly with various states
• Verify card network selector displays inline and dropdown variants
• Verify RTL layout support works correctly
• Verify PrimerSwiftUIBridgeViewController presents SwiftUI views in UIKit host

[github-actions]

	Warnings
⚠️	This PR doesn't seem to contain any updated Unit Test 🤔. Please consider double checking it.🙏
⚠️	> Pull Request size seems relatively large. If this Pull Request contains multiple changes, please split each into separate PR will helps faster, easier review.

Generated by 🚫 Danger Swift against 0c26606