feat(tabs): add beforeRemove event to allow canceling tab removal

[valorkin]

Summary

• Add beforeRemove event to TabDirective allowing cancellation of tab removal
• Developers can now show confirmation dialogs or prevent removal by calling event.preventDefault()
• Maintains full backward compatibility with existing removed event
• Works with both programmatic removal and keyboard (Delete key) removal

Test plan

• [x] beforeRemove event fires before tab removal
• [x] event.preventDefault() successfully cancels removal
• [x] removed event only fires if removal is not canceled
• [x] Keyboard deletion (Delete key) respects cancellation
• [x] Backward compatibility maintained for existing implementations
• [x] Unit tests cover all cancellation scenarios and edge cases
• [x] E2E tests verify behavior in real browser environment

🤖 Generated with Claude Code

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