packaging: add runtime Windows unpacked build

[ArcueidMP]

Summary

• Add a local Runtime Windows unpacked packaging command
• Add minimal electron-builder config for apps/runtime
• Add a Step 10.1 packaged Runtime smoke checklist
• Update README and dev-log with the Step 10.1 packaging scope

Scope

This PR produces a local unpacked Runtime build for validation.

It does not:

• package Maker
• bundle Python
• package the Python image pipeline
• create an installer
• create NSIS setup
• create a portable single exe
• publish artifacts
• create a GitHub Release binary
• create or modify tags
• add auto-updater support
• add zip export
• add persistent settings
• add Runtime launch-from-Maker
• add rembg
• add cloud APIs
• add system tray
• add multi-pet support
• add plugin support
• add new animation features

Verification

• git diff --check
• Hidden control character scan
• corepack pnpm typecheck
• corepack pnpm build
• corepack pnpm package:runtime:win:dir
• Test-Path release\runtime\win-unpacked
• Get-ChildItem release\runtime -Recurse -Filter "*.exe"
• Confirm generated release/ output is not staged or committed

Manual packaged Runtime smoke

To be performed after this packaging foundation is merged:

• Runtime exe launches
• Sample pet displays
• Animation advances
• Right-click menu opens
• Load Pet... opens folder picker
• Generated pet package can be loaded, if available
• Drag works
• Reset Position works
• Always on Top toggle works
• Exit works