fix(receiver): defer fullscreen transitions while display sleeps - #179

Summary

• defer SDL fullscreen transitions while the physical display is asleep
• retry the pending transition automatically after wake
• keep the Receiver network/render loop responsive during that interval
• restore windowed size and position only after a successful transition

Why

On macOS, SDL's Cocoa fullscreen operation may wait synchronously for a Space transition. If the iMac panel is asleep, that transition can stall and make the Receiver appear disconnected. Tracking the applied state separately lets the Receiver postpone only the window operation while continuing to serve the session.

Validation

• Receiver parser tests: 67 checks passed
• Receiver input queue tests: 562 checks passed
• Receiver profile tests: 13 checks passed
• full Receiver build completed successfully

This PR is limited to the fullscreen state machine and disconnect ordering needed for a reliable retry.