Replace custom collapse/toggle system with Bootstrap 5 Collapse API

The Spark Web UI has 40+ manual collapse implementations in webui.js using collapseTable(), toggleClass('collapsed'), and custom localStorage logic for state persistence.

Bootstrap 5's native Collapse API (data-bs-toggle="collapse", data-bs-target) handles all of this with zero JavaScript. This would:

• Remove ~100 lines of custom JS in webui.js (lines 32-55, 108-162)
• Eliminate manual arrow state management (.arrow-open, .arrow-closed)
• Simplify collapse usage across EnvironmentPage, JobPage, AllJobsPage, StoragePage, ExecutionPage
• Use BS5's built-in aria-expanded for accessibility

Part of SPARK-55760 (Spark Web UI Modernization)