fix: open popup on the same display as the source window in multi-monitor setups

[Copilot]

In multi-display environments, popup windows were always opening on the primary display instead of the display containing the source window.

Root Cause

getScreenSize() in the service worker context calls chrome.windows.getCurrent() to determine which display to use for bounds-checking. From a service worker, getCurrent() unreliably returns the last-focused window — often one on the primary display — rather than the window the user was actually interacting with. This caused adjustWindowPosition() to recalculate the popup position using the wrong display's bounds, snapping it to the primary monitor.

Changes

• screen.ts: Add optional hint?: { top: number; left: number } to getScreenSize(). When provided, the hint coordinates are used to identify the target display directly, bypassing getCurrent(). Falls back to existing getCurrent() behavior when no hint is given.

• chrome.ts: Pass the popup's target { top, left } coordinates as the hint when calling getScreenSize() in both openPopupWindow and openPopupWindowMultiple. These coordinates already originate from the content script's correct window position, so they reliably identify the right display.

// Before
const screenSize = await getScreenSize()

// After — use popup target coordinates to find the correct display
const screenSize = await getScreenSize({ top, left })

• screen.test.ts (new): Tests covering single/multi-display hint resolution, fallback to primary when hint is out-of-bounds, and non-service-worker path.