feat(spa): add 12 Blazor Razor files for Spa/Beauty POS vertical
Add new Spa POS vertical with appointment-based beauty/spa services:
Main POS screens (3 device variants):
- SpaDesktop.razor: Desktop 2-panel layout with service categories/grid + appointment panel
- SpaTablet.razor: Tablet touch-friendly layout with 340px appointment sidebar
- SpaMobile.razor: Mobile single-column with floating appointment button + bottom sheet
Workflow screens (9 files):
- CustomerLookup.razor: Search by phone/name with VIP tier display
- CustomerProfile.razor: Full profile with tier progress, visit history, rewards
- AppointmentBook.razor: Date picker, time slots grid (9:00-20:00), staff selection
- ServicePackage.razor: Package list with expandable details and savings
- ServiceCombo.razor: Active combos/promotions with flash sale timer
- StaffAssign.razor: Staff list with ratings, skills, availability status
- TherapistSchedule.razor: Calendar day view with horizontal timeline
- TreatmentTimer.razor: Circular countdown timer with extend/complete actions
- SpaJourney.razor: 5-step journey tracker (Check-in → Dịch vụ → Thực hiện → Thanh toán → Hoàn tất)
All files follow existing Cafe/Karaoke patterns:
- @layout PosLayout, @inherits PosBase
- Bilingual EN/VI comments, section separators
- CSS variables, Lucide icons, FormatPrice/NavigateTo helpers
- Vietnamese UI labels, VND prices, demo data
Co-authored-by: Velik <hongochai10@users.noreply.github.com>
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