[codex] Hook intrinsic content size invalidation

[muukii]

Summary

• Observe UIView.invalidateIntrinsicContentSize() for Rideau content descendants.
• Schedule a debounced self-sizing update when .autoPointsFromBottom content invalidates its intrinsic size.
• Enable the observer only when the Rideau configuration contains .autoPointsFromBottom.

Why

SwiftUI hosted content can change intrinsic size without an explicit requestRideauSelfSizingUpdate(). Hooking intrinsic invalidation lets auto snap points follow those updates automatically while keeping explicit requests as a fallback.

Validation

• Built RideauDemo for iOS Simulator with XcodeBuildMCP.
• Verified the SwiftUI autoPoints demo expands/shrinks without an explicit sizing request.