Adds Windows portable version

[hovancik]

closes #1148

[Copilot]

Pull request overview

This PR adds support for a Windows portable version of Stretchly, enabling users to run the application without installation. The implementation follows the established patterns used for other special distribution methods like Windows Store, Flatpak, and Snap.

Key changes include:

• Addition of portable build target in electron-builder configuration with custom artifact naming
• Implementation of portable environment detection using the PORTABLE_EXECUTABLE_DIR environment variable
• Configuration of data storage to use a local "Data" directory alongside the portable executable
• Automatic disabling of auto-update features for portable installations

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
package.json	Adds "portable" target to Windows build configuration and specifies custom artifact naming format
app/utils/utils.js	Implements insideWindowsPortable() detection function and exports it for use across the application
app/utils/defaultSettings.js	Updates default settings to disable auto-update features when running as portable version
app/utils/context-bridge-exposers.js	Exposes portable detection to renderer process via IPC bridge
app/preferences.html	Adds portable version display in debug info and hides "open at login" option for portable installations
app/preferences-renderer.js	Retrieves and displays portable version status in debug information panel
app/platform.js	Adds "portable" CSS class to body element when running as portable version
app/main.js	Implements portable data path initialization by creating and configuring a "Data" directory relative to the executable
app/css/commons.css	Adds CSS rule to hide elements with "portable-hidden" class when running in portable mode
CHANGELOG.md	Documents the new portable version feature