Added RDEPUBSelectionOverlayView and mounted it above the native text host so visible selection rendering is driven by page geometry.
Preserved the controller-owned selection contract: selections still normalize through RDEPUBSelection, absolute offsets still serialize through RDEPUBTextOffsetRangeInfo, and menu actions still flow through RDEPUBReaderController.
Clearing or reconfiguring a page now clears both overlay state and controller selection state.
Verification
build_sim for ReadViewDemo on iOS Simulator succeeded on 2026-05-22.
