refactor(saveload): Decouple result handling from game state

[bobtista]

Fixes #2998

GameState::saveGame and GameState::loadGame present their results directly through TheInGameUI and MessageBoxOk. This couples save serialization to interactive client UI and prevents non-interactive callers from handling results themselves.

Now save and load functions only return SaveCode results, while GUI callers present the existing success and error messages. Save functions can also return the resolved filename when one is generated automatically.

Todo:

[] Test creating and overwriting a normal save
[x] Test successful and failed save loading
[] Test mission-save feedback
[x] Replicate to Generals

[greptile-apps]

Greptile Summary

Refactors save/load result presentation out of GameState and into GUI-layer helpers.

• Adds optional resolved-filename outputs for normal and mission saves.
• Moves existing success and error feedback into SaveLoadFeedback.
• Updates popup and score-screen callers in both game targets.
• Registers the new helper files in both GameEngine builds.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failures remain.

Important Files Changed

Filename	Overview
Generals/Code/GameEngine/Source/Common/System/SaveGame/GameState.cpp	Removes direct UI presentation from persistence methods and returns structured save/load results with optional resolved filenames.
Generals/Code/GameEngine/Source/GameClient/GUI/GUICallbacks/SaveLoadFeedback.cpp	Centralizes the existing GUI messages and dialogs associated with save/load result codes.
Generals/Code/GameEngine/Source/GameClient/GUI/GUICallbacks/Menus/PopupSaveLoad.cpp	Captures save/load results and delegates their presentation to the new GUI helper.
Generals/Code/GameEngine/Source/GameClient/GUI/GUICallbacks/Menus/ScoreScreen.cpp	Presents mission-save results from the score-screen caller.
GeneralsMD/Code/GameEngine/Source/Common/System/SaveGame/GameState.cpp	Mirrors the decoupled persistence result handling for Zero Hour.
GeneralsMD/Code/GameEngine/Source/GameClient/GUI/GUICallbacks/SaveLoadFeedback.cpp	Mirrors the centralized save/load GUI feedback implementation for Zero Hour.

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