feat(react-native): true native iOS chat UI (fallback if WebView UX isn't sufficient)

[AimTune]

Goal

Provide a truly native iOS chat experience (SwiftUI/UIKit) as an alternative rendering backend for @chativa/rn-webview, for apps where the WebView-based widget doesn't meet the UX bar.

Background

@chativa/rn-webview (#6) currently ships a react-native-webview-based implementation: it embeds the existing web widget (@chativa/ui + @chativa/genui, loaded via the packages' existing CDN/global builds) inside a WebView and bridges events/config over postMessage. This reuses the web UI as-is and required no native re-implementation, but WebViews have known weak spots on iOS specifically — keyboard avoidance/resize timing, scroll/momentum feel, and animation smoothness can all fall short of a truly native screen.

This issue tracks the conditional fallback: only pursue this if the WebView approach proves insufficient in a real app.

Scope (to be refined when/if this is picked up)

• Evaluate the shipped WebView widget in a real iOS app first — keyboard behavior, scroll performance, animation smoothness, accessibility (VoiceOver) — and document concrete shortfalls before scoping native work.
• Decide the integration shape: a native Fabric component exposing a SwiftUI/UIKit chat view to @chativa/rn-webview, vs. a fully separate native iOS SDK usable outside RN entirely.
• Reuse @chativa/core's wire protocol / connector behavior conceptually (same ChativaSettings shape, same message/event model) even though the UI layer would be genuinely native Swift, not shared JS.
• GenUI: native equivalents of the built-in components, scoped down to whatever's actually needed once real usage data exists.

Acceptance

• Not scheduled — this issue exists to hold the decision and scope once/if the WebView approach is found insufficient. No acceptance criteria until scoped.

Out of scope (for now)

• Building anything here before the WebView widget (feat(react-native): @chativa/react-native package (native re-implementation) #6) ships and is evaluated in a real app.

[AimTune]

Package name update: the WebView implementation is published as @chativa/rn-webview (not @chativa/react-native — renamed to avoid future ambiguity if this issue's native UI ever ships alongside it under the @chativa/react-native name).