fix(web): make right panel tabs easier to scroll

[maria-rcks]

Horizontal overflow in the right-panel tabs was difficult to navigate with a Mac trackpad and inaccessible to ordinary mouse wheels. The strip now consumes either wheel axis consistently, keeps the Electron drag region away from the scrolling surface, and shows edge-aware scroll arrows only when tabs overflow. Verified with the web typecheck, focused lint and format checks, the existing RightPanelTabs tests, and real-app wheel and arrow passes at desktop and responsive sheet sizes.

Before

t3-tab-scroll-before.webm

After

t3-tab-scroll-after.webm

Built by gpt-5.6-sol in the Codex harness.

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Note

Low Risk
Localized UI interaction changes in RightPanelTabs with no auth, data, or API impact; main risk is wheel/drag-region edge cases on Electron.

Overview
Improves horizontal navigation when the right-panel tab strip overflows.

Wheel and trackpad: The tab list viewport now maps the dominant wheel delta (horizontal or vertical) into horizontal scroll, with preventDefault only when scrolling actually moves—so mouse wheels and awkward trackpad gestures can move tabs without relying on hidden scrollbars.

Overflow UI: A ResizeObserver plus scroll listeners track overflow and edge position; when tabs don't fit, left/right chevron buttons appear (disabled at the ends) and scroll by ~75% of the viewport width, respecting prefers-reduced-motion. Active-tab scrollIntoView runs only when overflow is present.

Electron title bar: The window drag region sits on the outer tab bar while the scrollable ScrollArea is marked no-drag, so users can scroll tabs without fighting window dragging on desktop.

^{Reviewed by Cursor Bugbot for commit 238a84d. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add scroll buttons and wheel-scroll support to RightPanelTabs

• Adds left and right scroll buttons to RightPanelTabs that appear when tabs overflow, disabling at the scroll boundaries.
• Adds a non-passive wheel listener to convert wheel input into horizontal tab scrolling, preserving pinch zoom and native page scrolling when no tab scroll occurs.
• Moves the Electron drag-region from the ScrollArea to the surrounding tab bar, marking the viewport and buttons as no-drag.
• Risk: The non-passive wheel listener calls preventDefault on the tab viewport in RightPanelTabs.tsx, which could block page scrolling if the container's overflow state changes.

^{Macroscope summarized 238a84d.}

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 2 potential issues.

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^{Reviewed by Cursor Bugbot for commit b586983. Configure here.}

[macroscopeapp]

Approvability

Verdict: Approved at 238a84d

Macroscope's review found this PR approvable — This is a localized right-panel UX adjustment that adds overflow-aware tab scrolling and controls without changing application data, defaults, or broader workflows. The runtime impact is confined to tab navigation and Electron title-bar hit-testing.

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