fix(ui): eliminate button overlapping on PC and mobile viewports with flex gaps

[ankhang0704]

Summary

• Fixed button collision and overlapping across desktop and mobile viewports.
• Configured .vault-relay-action-row, .vault-relay-actions-row, .vault-relay-filter-bar, and .vault-relay-conflict-actions\ as robust flex containers with explicit gap and margin separation.
• Set base buttons to \display: inline-flex; align-items: center; justify-content: center; box-sizing: border-box; margin: 0; white-space: nowrap;.
• Improved mobile responsive rules (@media (max-width: 480px)) with explicit vertical gaps (8-10px) and a two-column responsive chip layout for filter bars.
• Added automated test \C5-MOBILE-006\ to guard against future button layout regressions.