fix(ui): dismiss account menu on route change; stop dropdown swallowing nav clicks

[eliran-ops]

Summary

Two routing-adjacent dismissal bugs (SKY-822):

• 7 — Clicking a tab while a dropdown is open (e.g. Resources during the namespace dropdown) silently swallowed the click — no navigation, no apparent dropdown state change.
• 8 — Account menu (avatar dropdown) did not dismiss when navigating to a different page; persisted across page changes.

Root cause

• Bug 7: `NamespaceSelector` mounted a `fixed inset-0 z-[9998]` overlay above the entire viewport to detect outside clicks. The overlay's `onClick` closed the dropdown but, being above the nav, also ate the user's click — so Resources never received it.
• Bug 8: `UserMenu` lives in the app shell and survives router transitions, so its open `isOpen` state persisted across navigations. The previous code only listened for outside clicks via `mousedown`, not for route changes.

Fix

• New shared `useDismissable` hook in `packages/k8s-ui/src/hooks/` covering pointerdown-outside, Escape, and popstate dismissal in one declarative call. 7 unit tests pin the listener-attachment contract.
• `UserMenu` now uses `useDismissable`, so the menu closes on outside click, Escape, AND route change.
• `NamespaceSelector`'s click-eating backdrop is removed — the existing document-level `mousedown` listener already handled outside clicks cleanly. With the backdrop gone, a click on e.g. the Resources nav while the dropdown is open closes the dropdown AND navigates.
• `NamespaceSelector` also gets a small `popstate` listener so the dropdown closes on browser navigation.

Test plan

• `cd packages/k8s-ui && npm test` — 75 passed (7 new for `useDismissable`)
• `cd web && npm run tsc` — clean
• `cd web && npm run build` — clean

Made with Cursor

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Note

Medium Risk
Changes global event-listener behavior for overlay dismissal (including switching to document-level pointerdown and adding popstate handling), which could affect interaction timing or close overlays unexpectedly if container refs are misconfigured.

Overview
Introduces a reusable useDismissable hook (exported from packages/k8s-ui) that attaches global pointerdown, keydown (Escape), and popstate listeners to dismiss transient overlays, with opt-outs and container refs to treat multiple elements as “inside”.

Updates UserMenu to use useDismissable instead of its ad-hoc outside-click useEffect, fixing the menu staying open across route changes. Updates NamespaceSelector to close on popstate and removes the viewport-wide backdrop so outside clicks dismiss without swallowing the underlying navigation click.

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[eliran-ops]

@nadaverell @hisco — ready for review. Cursor bugbot found 1 issue on an earlier commit (addEventListener('mousedown') instead of pointerdown); fixed in commit 0fc6ff6. Cursor Bugbot SUCCESS on current HEAD.