fix(tabs): follow-ups from the wheel-scroll review (#2095) #2103

Follow-up to #2095 (non-blocking findings from the merge pass's review).

• Diagonal trackpad input can move the strip the wrong way (src/components/TabStrip.tsx, wheel handler): a vertical-dominant event that also carries horizontal motion is cancelled and translated from deltaY alone. At scrollLeft=400, deltaX=-20, deltaY=40 moves the strip to 440, opposite to the swipe's horizontal part. Reproduced by Codex in a component unit fixture. Suggested: leave events with deltaX !== 0 to the browser, and cover vertical-dominant diagonals with matching and opposing signs.
• Fragile rebinding: the wheel listener is reattached only when [shown, tabsHidden, end === undefined] changes; a callback ref would survive a future wrapper element.
• Firefox line-mode branch runs less often than the comment says (deltaY is read before deltaMode).
• Wheel at the strip's end is still cancelled, so a future scrolling parent would not get it.
• Open tab menu or drag insertion line can drift while the strip scrolls (also true for trackpad/touch scrolling before fix(tabs): scroll an overflowing tab strip sideways with a vertical mouse wheel #2095).
• One waitForFunction in scripts/tab-overflow-regression.ts relies on Playwright's 30 s default timeout.