feature(headless): Add ParticleSystemManagerDummy for headless mode

[bobtista]

Summary

• Adds ParticleSystemManagerDummy class in Core/GameEngine/Include/GameClient/ParticleSys.h with no-op implementations for headless mode
• GameEngine.cpp uses dummy when m_headless is true
• Empty crc/xfer/loadPostProcess to skip particle system block in saves

Related

Split from #2139 per @xezon's suggestion to review each dummy class separately.

[greptile-apps]

Greptile Overview

Greptile Summary

This PR adds ParticleSystemManagerDummy to enable headless mode operation without particle system rendering overhead.

Changes:

• Added ParticleSystemManagerDummy class in ParticleSys.h that inherits from ParticleSystemManager
• Overrides all required virtual methods with no-op implementations
• Empty crc(), xfer(), and loadPostProcess() methods skip particle system data in save files
• Both Generals and GeneralsMD GameEngine.cpp conditionally instantiate the dummy when TheGlobalData->m_headless is true

Implementation Quality:

• Follows the same pattern as existing dummy classes (AudioManagerDummy, RadarDummy)
• All pure virtual methods are properly overridden
• Memory allocation uses NEW macro consistent with other dummy class allocations
• The approach correctly eliminates particle system processing overhead for headless servers

Confidence Score: 5/5

• This PR is safe to merge with no issues found
• The implementation correctly follows established patterns for dummy classes in headless mode, all pure virtual methods are properly overridden with appropriate no-op implementations, and the conditional instantiation logic is consistent with existing AudioManagerDummy and RadarDummy implementations
• No files require special attention

Important Files Changed

Filename	Overview
Core/GameEngine/Include/GameClient/ParticleSys.h	Added ParticleSystemManagerDummy class with no-op implementations of all required virtual methods for headless mode
Generals/Code/GameEngine/Source/Common/GameEngine.cpp	Uses ParticleSystemManagerDummy when m_headless is true, consistent with existing AudioManagerDummy and RadarDummy patterns
GeneralsMD/Code/GameEngine/Source/Common/GameEngine.cpp	Uses ParticleSystemManagerDummy when m_headless is true, consistent with existing AudioManagerDummy and RadarDummy patterns

Sequence Diagram

sequenceDiagram
    participant GE as GameEngine
    participant GD as TheGlobalData
    participant Factory as createParticleSystemManager()
    participant Dummy as ParticleSystemManagerDummy
    participant PSM as TheParticleSystemManager

    GE->>GD: Check m_headless flag
    alt m_headless == true
        GE->>Dummy: NEW ParticleSystemManagerDummy
        Dummy-->>PSM: Initialize as singleton
        Note over Dummy: All methods are no-ops:<br/>getOnScreenParticleCount() returns 0<br/>doParticles() does nothing<br/>queueParticleRender() does nothing<br/>crc/xfer/loadPostProcess() skip save data
    else m_headless == false
        GE->>Factory: createParticleSystemManager()
        Factory-->>PSM: Initialize full implementation
        Note over PSM: Normal particle system<br/>with rendering and updates
    end
    GE->>PSM: initSubsystem(TheParticleSystemManager)

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