test: add Dropdown component tests

[Copilot]

Adds comprehensive Cypress component tests for the Dropdown component to prevent regressions.

Test Coverage

• Basic rendering: Default trigger button, custom slots, button props
• Interactions: Menu open/close, item clicks, event handlers
• Layout options: Placements (left/right/center), side/offset positioning
• Advanced features: Grouped options, submenus (including nested), switch items, conditional filtering
• Edge cases: Disabled items, themed items (red), icon placeholder alignment

Follows existing patterns from Badge and Button component tests.

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[Copilot]

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• download.cypress.io
  • Triggering command: /usr/local/bin/node node dist/index.js --exec install (dns block)
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