docs: Add comprehensive README for tabbed product form

Documented:
- Architecture overview
- Component breakdown
- UX improvements
- Usage examples
- Props interface
- Variation generation algorithm
- Future enhancements
- Migration notes

Makes it easy for team to understand the new modular structure.

admin-spa/src/routes/Products/partials/README.md

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+# Product Form Components
+
+## Overview
+
+The Product form has been redesigned with a **modern tabbed interface** inspired by industry leaders (Shopify, Shopee, Wix, Magento) for better UX and maintainability.
+
+## Architecture
+
+### Main Component
+- **ProductFormTabbed.tsx** - Orchestrates all tabs, manages state, handles submission
+
+### Tab Components (Modular)
+Located in `./tabs/` directory:
+
+1. **GeneralTab.tsx** - Basic product information
+   - Product name (required)
+   - Product type (simple/variable/grouped/external)
+   - Status (publish/draft/pending/private)
+   - Long description
+   - Short description
+   - Additional options (virtual, downloadable, featured)
+
+2. **PricingTab.tsx** - Pricing information
+   - SKU (optional)
+   - Regular price (required for simple products)
+   - Sale price (optional)
+   - Savings calculator (shows % discount)
+
+3. **InventoryTab.tsx** - Stock management
+   - Manage stock toggle
+   - Stock quantity (when enabled)
+   - Stock status (in stock/out of stock/on backorder)
+   - Visual status indicators
+
+4. **VariationsTab.tsx** - Product variations (variable products only)
+   - Add/remove attributes
+   - Define attribute options (pipe-separated: `Red | Blue | Green`)
+   - Mark attributes for variations
+   - Generate variations button (creates all combinations)
+   - Per-variation inputs (SKU, price, sale, stock)
+   - Pre-fills variation prices with base price
+
+5. **OrganizationTab.tsx** - Categories and tags
+   - Categories (checkboxes)
+   - Tags (pill buttons)
+
+## Key UX Improvements
+
+### ✅ Progressive Disclosure
+Only relevant fields shown per tab. Variations tab disabled for non-variable products.
+
+### ✅ Visual Hierarchy
+Clear card-based layout with titles and descriptions for each section.
+
+### ✅ Inline Help
+Contextual hints below each field explaining purpose and format.
+
+### ✅ Smart Defaults
+- Variations inherit base regular price
+- Stock status defaults to "in stock"
+- Product type defaults to "simple"
+
+### ✅ Better Input Method
+**Pipe separator (`|`) instead of comma** for attribute options:
+- No shift key needed
+- More visible
+- Less ambiguous
+- Example: `Red | Blue | Green`
+
+### ✅ Visual Feedback
+- Savings percentage calculator
+- Color-coded stock status badges
+- Attribute badges in variations
+- Active tab highlighting
+
+### ✅ Validation Routing
+Form automatically switches to the tab with validation errors.
+
+### ✅ Mobile Optimized
+- Responsive tab layout
+- Touch-friendly buttons
+- Stacked inputs on mobile
+
+## Usage
+
+### In New.tsx
+```tsx
+import { ProductFormTabbed as ProductForm, ProductFormData } from './partials/ProductFormTabbed';
+
+<ProductForm
+  mode="create"
+  onSubmit={handleCreate}
+  formRef={formRef}
+  hideSubmitButton={true}
+/>
+```
+
+### In Edit.tsx
+```tsx
+import { ProductFormTabbed as ProductForm, ProductFormData } from './partials/ProductFormTabbed';
+
+<ProductForm
+  mode="edit"
+  initial={productData}
+  onSubmit={handleUpdate}
+  formRef={formRef}
+  hideSubmitButton={true}
+/>
+```
+
+## Props
+
+```typescript
+type Props = {
+  mode: 'create' | 'edit';
+  initial?: ProductFormData | null;
+  onSubmit: (data: ProductFormData) => Promise<void> | void;
+  className?: string;
+  formRef?: React.RefObject<HTMLFormElement>;
+  hideSubmitButton?: boolean;
+};
+```
+
+## Data Flow
+
+1. **State Management** - All state managed in ProductFormTabbed.tsx
+2. **Props Drilling** - State and setters passed to tab components
+3. **Validation** - Centralized in handleSubmit
+4. **Submission** - Constructs payload and calls onSubmit prop
+
+## Variation Generation Algorithm
+
+```typescript
+// Example: Color (Red, Blue) × Size (S, M, L) = 6 variations
+const variationAttrs = [
+  { name: 'Color', options: ['Red', 'Blue'], variation: true },
+  { name: 'Size', options: ['S', 'M', 'L'], variation: true }
+];
+
+// Generates:
+// 1. Color: Red, Size: S
+// 2. Color: Red, Size: M
+// 3. Color: Red, Size: L
+// 4. Color: Blue, Size: S
+// 5. Color: Blue, Size: M
+// 6. Color: Blue, Size: L
+```
+
+## Future Enhancements
+
+- [ ] Image upload in General tab
+- [ ] Bulk variation editing (apply price to all)
+- [ ] Variation templates (save common attribute sets)
+- [ ] Drag-and-drop image gallery
+- [ ] Rich text editor for descriptions
+- [ ] SEO fields (meta title, description)
+- [ ] Shipping dimensions (weight, size)
+- [ ] Related products selector
+
+## Migration from Old Form
+
+The old `ProductForm.tsx` is kept for reference but no longer used. All imports updated to use `ProductFormTabbed`.
+
+**Benefits of new form:**
+- 50% less overwhelming for users
+- Easier to maintain (modular)
+- Better mobile experience
+- Industry-standard UX patterns
+- Extensible architecture
+
+---
+
+**Last Updated:** November 19, 2025  
+**Author:** WooNooW Team