feat(app): add membership edit modal with tab UI
- Replace detail-only modal with tab-based (detail/edit) modal
- Detail tab shows membership card info, stats, and action buttons
- Edit tab provides form to modify card type, remaining times, start/expire dates
- Add loadDetailMembership, switchTab, initEditForm, onSaveMembership, onClearMembership functions
- Add computed isTimeBasedCard for edit form conditional rendering
- Append new styles for modal-header, tab-bar, membership-card, edit-form, etc.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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