[codex] Add safe instance management features

[ExtremestoneGG]

What changed

• Makes CurseForge clearly optional while keeping Modrinth, Forge, NeoForge, Java, and local launcher features available without an API key.
• Adds existing Minecraft installation scanning with version, loader, mods, worlds, resource packs, shaders, size, and VEX ownership summaries.
• Adds full instance backups from the Library.
• Adds safe Modrinth modpack update checks and in-place updates with an automatic backup first.
• Adds a feature roadmap based on useful Modrinth App and Prism Launcher workflows.
• Fixes the mobile sidebar opening behavior and protects long paths from breaking the settings layout.
• Bumps VEX to 0.8.0.

Why

The CurseForge API key was being confused with Forge loader support. Forge and NeoForge do not require that key. This update separates those concepts and adds the highest-value instance management features without introducing destructive automatic behavior.

Validation

• cargo fmt --check
• cargo check
• npm run build
• Windows NSIS installer build
• Self-contained portable build and launch smoke test
• Responsive UI verification at 1280x720 and 800x600