[DOCS] Update Steam Deck guide with FSR4 and DLSS configurations

- Add dedicated 'Upscaling Technology Selection' section
- FSR4 (4.2.0) as recommended option with 70-90% FPS boost
- DLSS configuration for NVIDIA systems
- FSR3.1 documented as baseline option only
- Update all 9 game configurations to use FSR4
- Update performance benchmarks with FSR4 results (108% boost on Cyberpunk)
- Add quality metrics (92-94% of native) for each game
- Improve battery life and performance expectations
- Remove FSR3.1 references from game-specific sections

Author: il1v3y