Add desktop launcher tuning flags and modernization roadmap

[awest813]

Motivation

• Provide runtime knobs to improve compatibility and performance without changing code by exposing common launcher options.
• Make the launcher more discoverable and easier to test for different GPU/OS configurations by adding a -help command and windowed/quality flags.
• Capture a practical modernization roadmap to guide follow-up work across modernization, compatibility, performance, and QoL.

Description

• Extended DesktopLauncher to accept and apply new CLI options including -help/--help/-h, -windowed [width height] (alias -window preserved), -vsync/-novsync, -fps <value>, and -msaa <samples>, with defaults and safe parsing fallbacks.
• Added DEFAULT_WINDOWED_WIDTH/DEFAULT_WINDOWED_HEIGHT constants and utility methods isInteger and parseIntWithFallback to validate numeric arguments and print fallback warnings.
• Wired parsed values into LwjglApplicationConfiguration (width, height, fullscreen, vSyncEnabled, samples, foregroundFPS, backgroundFPS) so users can tune MSAA, FPS caps, and VSync from the launcher.
• Updated README.md to document the new launcher flags and added docs/ENGINE_MODERNIZATION_ANALYSIS.md containing a phased roadmap for modernization, compatibility, performance, and QoL improvements.

Testing

• Attempted to compile the desktop module with ./gradlew :desktop:compileJava to validate the change in this environment, but the build failed due to a local Gradle/Groovy vs JDK mismatch (Unsupported class file major version 65) unrelated to the launcher logic.
• No other automated tests were executed in this environment; the change is intentionally low-risk and limited to argument parsing and launcher wiring.

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Codex Task