fix: Disable SteamManager autoload until GodotSteam is properly installed

Steam Integration Postponed:
- Remove SteamManager from autoloads (was causing parse errors)
- Remove [steam] config section
- GodotSteam plugin not yet installed in CI/CD environment
- Pre-build validation correctly caught the missing dependency

SteamManager code remains in godot/autoload/steam_manager.gd for future use.
Will re-enable once GodotSteam plugin is properly installed across all build
environments.

Validation now passes:
- All GDScript parse checks: PASS
- Scene file structure: PASS
- Missing resources: PASS
- Autoload scripts: PASS

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: PipFoweraker

godot/project.godot

@@ -28,7 +28,6 @@ LogExporter="*res://autoload/log_exporter.gd"
 IconLoader="*res://autoload/icon_loader.gd"
 MusicManager="*res://autoload/music_manager.gd"
 VerificationTracker="*res://autoload/verification_tracker.gd"
-SteamManager="*res://autoload/steam_manager.gd"
 GameManager="*res://scripts/game_manager.gd"
 
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