fix(tui): polish cluster browser interactions

[vincentkoc]

Summary

• split cluster/member action-menu contexts so right-click menus match the selected pane
• tune TUI row colors: open rows stay yellow, closed rows stay greyed, selected rows use a quieter focus tint
• preserve the loaded cluster viewport across auto-refresh instead of collapsing to a 20-row subset
• let cluster/member age headers toggle newest/oldest sort direction
• buffer fast trackpad wheel bursts so scroll input does not keep drifting after the gesture

Tests

• go test ./...
• git diff --check origin/main..HEAD

Still draft for visual/manual pass in the TUI.