fix(watchlist): make tabs scrollable at narrow widths

[jakearmstrong59]

Summary

Fix the Watchlist page tab row so all tabs remain reachable when the viewport is too narrow to display them at once.

The Watchlist tabs already used MUI's scrollable tab variant, but the tab container was not constrained tightly enough at narrow non-mobile widths. This could leave overflowed tabs hidden and difficult or impossible to select.

This update:

• Enables mobile scroll buttons for the Watchlist tab row
• Constrains the Tabs component to the visible width
• Adds horizontal overscroll containment
• Styles scroll buttons consistently with the existing theme
• Preserves existing tab labels, badges, and URL tab behavior

Related Issues

Fixes #915

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Screenshots

Record_2026_04_30_14_52_42_864.mp4

Record_2026_04_30_14_54_52_650.mp4

Checklist

• New components are modularized/separated where sensible
• Uses predefined theme (e.g. no hardcoded colors)
• Responsive/mobile checked
• Tested against the test API
• npm run lint passes
• npm run build passes
• Screenshots included for any UI/visual changes