fix: make context-menu double-click reliable on Linux/macOS (#24, #26, #12)

[furkanyolal]

Problem

When gestures are bound to the right button, opening the context menu on Linux/macOS takes 3–4 right-clicks instead of the intended double-click (#24, #26, #12).

On these platforms Chromium fires the contextmenu event on mouse-down, so the first right-click is necessarily reserved for gesture detection and the menu is meant to open on a second click. The detection of that second click, however, required it to land within 300 ms AND within the gesture distanceThreshold (10 px) of the first:

const withinTime = now - this._lastClick.time < doubleClickThreshold; // 300 ms
const withinDist = getDistance(...) < this.distanceThreshold;          // 10 px (gesture threshold)

A normal-paced double-click easily exceeds 300 ms, so the second click falls outside the window, gets suppressed again, and _lastClick resets to "now" — the user has to keep clicking until two happen to land < 300 ms apart. Reusing the tiny gesture threshold for the click-distance check makes it even more fragile.

Fix

Keep the existing (and, on Chromium, unavoidable) double-click model, but make it reliable:

• Configurable, more forgiving time window — replace the hardcoded 300 ms with Settings.Gesture.contextMenuTimeout (default 400 ms), exposed in the advanced gesture settings so users who want a longer window can set one. This directly addresses the maintainer's note in When rocker gestures are on, right clicking on webpages requires double right clicking. #12/Context menu appears after every gesture #18 about adding an option to control this behavior.
• Decouple the double-click distance from the gesture distanceThreshold via a dedicated, more generous constant (24 px), so minor cursor jitter between the two clicks no longer resets the sequence.
• Clear the pending first-click when a real gesture starts, so a gesture's suppressed contextmenu can't be mistaken for the second click of a context-menu double-click.

No behavioural change on Windows (where contextmenu fires on mouse-up and single-click already works) — only the non-Windows double-click path and its new tunable are affected. Defaults are backward-compatible.

Testing

Built with npm run dist and loaded unpacked in Brave 1.91.171 / Chromium 149 on KDE Plasma 6.6 Wayland:

• Normal-paced double right-click now opens the context menu reliably (previously 3–4 tries).
• Right-button gestures (left/right drag) still work, with the trace drawn.
• No stray context menu appears after completing a gesture.
• New "Context menu timeout" setting appears under advanced gesture settings and takes effect live.

Note

This does not (and cannot) provide single-right-click context menus with right-button gestures on Chromium — that requires the menu to fire on mouse-up, which Chromium does not expose to extensions (see chromium issue 41029299). This PR only makes the existing double-click compromise dependable.