Implement player stats HUD and mechanics
- Replace stats icon with new StatsHud UI component.
- Bind HP, mana, hunger, thirst, and energy percentage callbacks to StatsHud.
- Return 0.0 for mana percentage if the player uses a weapon requiring more mana than available.
- Halve character movement velocity when hunger or thirst is depleted.
- Make walk footstep SFX less often when hunger or thirst is depleted.
- Regenerate player HP slowly over time.
- Implement StatsHud class rendering five radial stat indicator arcs.
- Define stats-hud-ui.frag fragment shader to color code status indicators and handle blinking at zero values.
- Register stats-hud-ui.frag shader in assets.
- Update TODO list for survival stats framework, mechanics, and UI.