fix: make apps work in built copies of goose

[alexhancock]

The old code in the launch-app IPC handler tried to construct the standalone app URL by extracting the origin from the current window's URL:

const currentUrl = launchingWindow.webContents.getURL();
const baseUrl = new URL(currentUrl).origin;
const standaloneUrl = `${baseUrl}/#/standalone-app?...`;

• In development (just run-ui), the main window URL is http://localhost:5173/..., so origin returns http://localhost:5173
• In production (built app), the main window loads from a file:// URL like file:///C:/path/to/app/index.html#/.... For file:// URLs, new URL(...).origin returns the string "null"

This caused the standalone app window to try loading a URL like null/#/standalone-app?.... The fix constructs the URL the same way the main window URL is constructed elsewhere in the codebase:

const url = MAIN_WINDOW_VITE_DEV_SERVER_URL
  ? new URL(MAIN_WINDOW_VITE_DEV_SERVER_URL)
  : pathToFileURL(path.join(__dirname, `../renderer/${MAIN_WINDOW_VITE_NAME}/index.html`));

• In dev mode: Uses the Vite dev server URL (http://localhost:5173)
• In production: Uses pathToFileURL() to properly construct a file:// URL pointing to the bundled HTML file

[Copilot]

Pull request overview

This PR fixes a critical bug preventing standalone app windows from loading in production builds of the goose desktop application. The issue occurred because the old code extracted the URL origin from the launching window, which returns the string "null" for file:// URLs in production builds, resulting in invalid URLs like "null/#/standalone-app?...".

Changes:

• Replaced broken URL origin extraction with the same URL construction pattern used for main window and launcher window creation
• Improved query parameter encoding by using URLSearchParams instead of manual encodeURIComponent calls
• Added comment explaining the fix for future maintainers

[jamadeo]

I'd delete the comment about "fixing", since this is how it should have always been really

[DOsinga]

drop the comments? I don't know how this is related to Windows builds

[DOsinga]

this is literalyy the same as for the main window indeed, can we not just reuse that?