Consolidate Hello and Hello-iOS into a single Hello.c

Replace the traditional main()+event-loop with SDL_MAIN_USE_CALLBACKS,
which works on all platforms (desktop and mobile) as the modern SDL3 way.

- One SDL_PLATFORM_IOS guard controls window size and fullscreen flag;
  everything else is identical across platforms
- Register both the compile-time EXAMPLES path (dev builds) and
  SDL_GetBasePath() (installed / iOS bundle) as resource paths
- Use non-blocking acquireSwapchainTexture everywhere; gracefully skips
  frames when the swapchain is unavailable (window minimised, app
  backgrounded on iOS)
- Delete Examples/Hello-iOS/Hello-iOS.c; update Xcode iOS target to
  compile Hello.c directly
- Remove HelloiOS from Makefile.am (now identical to Hello)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jdolan