feat: add show option to BrowserWindow for deferred visibility

[ragamufin]

Summary

Adds a show option to BrowserWindow that controls whether the window is displayed immediately on creation. Defaults to true (current behavior).

When show: false is passed, the window is created but showWindow() is skipped. The window can be made visible later by calling window.show().

Motivation

Electron's BrowserWindow supports show: false, which is commonly used for:

• E2E testing: Playwright/test frameworks can spawn app instances that appear in the dock without stealing focus or flashing windows
• Splash screens: Create a window, load content, then show when ready
• Background windows: Create windows that start hidden until needed

This is a small, backwards-compatible change — existing code that doesn't pass show continues to work identically.

Changes

• BrowserWindow.ts: Added show?: boolean to WindowOptionsType, added show: true to default options, passed through constructor → init → createWindow
• native.ts: Added show?: boolean to createWindow params, wrapped showWindow() in if (params.show !== false) guard

Usage

// Window appears immediately (default, unchanged behavior)
const win = new BrowserWindow({ title: "My App", url: "..." });

// Window created but not shown
const hidden = new BrowserWindow({ title: "Hidden", url: "...", show: false });

// Show it later
hidden.show();

Testing

Tested locally on macOS ARM64:

• new BrowserWindow() with no show option → window appears immediately ✓
• new BrowserWindow({ show: false }) → window created but not visible ✓
• window.show() on hidden window → window becomes visible ✓
• No crashes or errors ✓