Fix Expo user attribute removal docs

[dcrawbuck]

Summary

Clarifies the shared Setting User Attributes docs so each SDK sees platform-specific callback and attribute removal guidance.
The Expo page now tells users to unset attributes with null, explains that undefined keys are ignored, and notes that nullable attributes require expo-superwall 1.0.5 or later.
The Flutter page no longer shows a non-compiling null removal example because its SDK currently accepts non-null Object values.

Validation

• bun run build:cf
• bun test
• /Users/dcrawbuck/.agents/skills/autoreview/scripts/autoreview --mode local

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Note

Low Risk
Documentation-only edits with no runtime, auth, or data-path changes.

Overview
Updates Setting User Attributes so callback notes, intro wording, and attribute removal guidance are split per SDK instead of one shared iOS-style block.

Expo now documents paywall-driven attribute updates via onUserAttributesChange in useSuperwallEvents, removal with null (with undefined keys ignored on the bridge), a update({ profilePic: null }) example, and a 1.0.5+ requirement for nullable attributes.

Flutter explicitly states the SDK only accepts non-null values and does not support deletion via null, removing misleading removal examples.

iOS/Android retain nil / null unset examples under platform tabs; the generic intro now refers to a dictionary or object rather than only [String: Any?].

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Document a real Expo attribute-change hook

For Expo users trying to react to a paywall Set user attributes action, this points them to onUserAttributesChange, but the current expo-superwall event surface does not define or dispatch that callback: I checked upstream src/SuperwallEventCallbacks.ts and src/internal/superwallEventBridge.ts, and the callback list/switch only includes the existing paywall, subscription, log, purchase, and custom-callback events. Following this quickstart would therefore compile against a nonexistent callback (or never fire if forced through types); please document the supported Expo path or add the bridge before referencing it here.

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