[WebUI] Session list requires two taps to open a session on mobile

Bug Description

On mobile, the first tap on a session row in the sidebar has no visible effect. A second tap on the same row is required before the session actually opens. The list reads as unresponsive.

Steps to Reproduce

1. Open the WebUI on a phone (iPhone Air, iOS 27).
2. Open the sidebar.
3. Tap a session row once: nothing happens.
4. Tap the same row again: the session opens.

Expected Behavior

A single tap opens the session.

Additional Context

Client: iPhone Air, iOS 27.

Cause not yet identified. Candidates worth ruling out, all verified to exist in the current tree:

• The row is a button carrying draggable={canDragSession} (webui/src/components/ChatList.tsx). Touch handling of draggable elements on iOS can consume the first tap.
• The row's trailing action menu trigger is opacity-0 with group-hover:opacity-100 and is not gated behind @media (hover: hover) (webui/src/components/ChatList.tsx). It is h-6 w-6 at the trailing edge and remains hit-testable while invisible, so the first tap can either land on it or transition the hover state instead of activating the row. Note that .settings-hover in webui/src/globals.css does gate hover styles behind @media (hover: hover), so the two treatments are inconsistent.
• The mobile sidebar lives in SheetContent (webui/src/App.tsx), and webui/src/components/ui/sheet.tsx was patched for programmatic open/close in #4494. Worth checking whether the first tap is consumed while the drawer is still animating.
• A first tap that only moves focus can also trigger a re-render. In the mobile drawer the search button is focused on open and shows a tooltip that closes on blur (see the companion sidebar-tooltip issue). If that re-render lands between pointerdown and click, the click may be lost. That would make both issues share a root cause, in which case they should be fixed together.

Also worth confirming whether this reproduces in mobile Safari without installation, and on Android.