fix: Zone modal blank + Tax route redirect + Simplify notifications (Shopify style)

## 1. Fixed Blank Zone Modal ✅
**Problem:** Console error "setIsModalOpen is not defined"

**Fix:**
- Removed unused isModalOpen/setIsModalOpen state
- Use selectedZone state to control modal open/close
- Dialog/Drawer opens when selectedZone is truthy
- Simplified onClick handlers

## 2. Fixed Tax Settings Blank Page ✅
**Problem:** URL /settings/taxes (plural) was blank

**Fix:**
- Added redirect route from /settings/taxes → /settings/tax
- Maintains backward compatibility
- Users can access via either URL

## 3. Simplified Notifications (Shopify/Marketplace Style) ✅
**Philosophy:** "App for daily needs and quick access"

**Changes:**
- ✅ Removed individual "Edit in WooCommerce" links (cluttered)
- ✅ Removed "Email Sender" section (not daily need)
- ✅ Removed redundant "Advanced Settings" link at bottom
- ✅ Simplified info card with practical tips
- ✅ Clean toggle-only interface like Shopify
- ✅ Single link to advanced settings in info card

**What Shopify/Marketplaces Do:**
- Simple on/off toggles for each notification
- Brief description of what each email does
- Practical tips about which to enable
- Single link to advanced customization
- No clutter, focus on common tasks

**What We Provide:**
- Toggle to enable/disable each email
- Clear descriptions
- Quick tips for best practices
- Link to WooCommerce for templates/styling

**What WooCommerce Provides:**
- Email templates and HTML/CSS
- Subject lines and content
- Sender details
- Custom recipients

Perfect separation of concerns! 🎯

admin-spa/src/App.tsx

@@ -430,6 +430,7 @@ function AppRoutes() {
       <Route path="/settings/payments" element={<SettingsPayments />} />
       <Route path="/settings/shipping" element={<SettingsShipping />} />
       <Route path="/settings/tax" element={<SettingsTax />} />
+      <Route path="/settings/taxes" element={<Navigate to="/settings/tax" replace />} />
       <Route path="/settings/local-pickup" element={<SettingsLocalPickup />} />
       <Route path="/settings/checkout" element={<SettingsIndex />} />
       <Route path="/settings/customers" element={<SettingsIndex />} />