v0.6.2 — NavigationMenu hover: sibling-link close + grace delay

NavigationMenu hover behavior, matching Radix/shadcn (#33):

• Sibling links close the panel: hovering a plain top-level link (one without a panel) now closes an open sibling's panel — previously the panel stayed open until the pointer left the entire nav. Links inside a panel are unaffected (they resolve to the open menu, so the panel stays).
• 150ms grace delay on hover closes: the natural diagonal pointer path from a trigger to its panel — which can clip a sibling link or briefly exit the nav — no longer slams the panel shut. Closes arm a short timer; reaching the panel or any trigger cancels it. Resting on a sibling, leaving the nav, Escape, and trigger-to-trigger switching all still behave as expected (the latter two instantly).

Menubar is unaffected (its top-level items are all triggers). Suite green (263 runs); verified with timing-controlled pointer paths in WebKit 26.5 and interactively in Chrome on the theme-builder page that surfaced the report.