feat: Add in-app documentation system

Phase 1: Core Documentation
- Created docs/ folder with 8 markdown documentation files
- Getting Started, Installation, Troubleshooting, FAQ
- Configuration docs (Appearance, SPA Mode)
- Feature docs (Shop, Checkout)
- PHP registry with filter hook for addon extensibility

Phase 2: Documentation Viewer
- DocsController.php with REST API endpoints
- GET /woonoow/v1/docs - List all docs (with addon hook)
- GET /woonoow/v1/docs/{slug} - Get document content
- Admin SPA /help route with sidebar navigation
- Markdown rendering with react-markdown
- Added Help & Docs to More page for mobile access

Filter Hook: woonoow_docs_registry
Addons can register their own documentation sections.

docs/configuration/spa-mode.md

@@ -0,0 +1,139 @@
+# SPA Mode
+
+Understanding and configuring WooNooW's SPA (Single Page Application) mode.
+
+## What is SPA Mode?
+
+SPA Mode controls how WooNooW handles your WooCommerce pages. It determines whether visitors experience the modern SPA interface or traditional WooCommerce templates.
+
+---
+
+## Available Modes
+
+### Full Mode (Recommended)
+
+**All WooCommerce pages redirect to the SPA.**
+
+When a visitor navigates to:
+- `/shop` → Redirects to `/store/shop`
+- `/product/example` → Redirects to `/store/product/example`
+- `/cart` → Redirects to `/store/cart`
+- `/checkout` → Redirects to `/store/checkout`
+- `/my-account` → Redirects to `/store/my-account`
+
+**Benefits**:
+- Instant page transitions
+- Modern, consistent UI
+- Better mobile experience
+- Smooth animations
+
+**Best for**:
+- New stores
+- Stores wanting a modern look
+- Mobile-focused businesses
+
+### Disabled Mode
+
+**WooCommerce uses its native templates.**
+
+WooCommerce pages work normally with your theme's templates. WooNooW admin features still work, but the customer-facing SPA is turned off.
+
+**Benefits**:
+- Keep existing theme customizations
+- Compatibility with WooCommerce template overrides
+- Traditional page-by-page navigation
+
+**Best for**:
+- Stores with heavy theme customizations
+- Testing before full rollout
+- Troubleshooting issues
+
+---
+
+## Switching Modes
+
+### How to Switch
+
+1. Go to **WooNooW → Appearance → General**
+2. Find **SPA Mode** setting
+3. Select your preferred mode
+4. Click **Save Changes**
+
+### What Happens When Switching
+
+**Switching to Full**:
+- WooCommerce pages start redirecting
+- SPA loads for shop experience
+- No data is changed
+
+**Switching to Disabled**:
+- Redirects stop immediately
+- WooCommerce templates take over
+- No data is changed
+
+> **Note**: All your products, orders, and settings remain unchanged when switching modes.
+
+---
+
+## URL Structure
+
+### Full Mode URLs
+
+```
+https://yourstore.com/store/              → Home/Shop
+https://yourstore.com/store/shop          → Shop page
+https://yourstore.com/store/product/slug  → Product page
+https://yourstore.com/store/cart          → Cart
+https://yourstore.com/store/checkout      → Checkout
+https://yourstore.com/store/my-account    → Account
+```
+
+### Disabled Mode URLs
+
+Standard WooCommerce URLs:
+```
+https://yourstore.com/shop/               → Shop page
+https://yourstore.com/product/slug        → Product page
+https://yourstore.com/cart/               → Cart
+https://yourstore.com/checkout/           → Checkout
+https://yourstore.com/my-account/         → Account
+```
+
+---
+
+## SEO Considerations
+
+### Full Mode SEO
+
+- WooCommerce URLs (`/product/slug`) remain in sitemaps
+- When users click from search results, they're redirected to SPA
+- Meta tags are generated dynamically for social sharing
+- 302 (temporary) redirects preserve link equity
+
+### Disabled Mode SEO
+
+- Standard WooCommerce SEO applies
+- No redirects needed
+- Works with Yoast SEO, RankMath, etc.
+
+---
+
+## Troubleshooting
+
+### Redirects Not Working
+
+1. **Flush Permalinks**: Go to Settings → Permalinks → Save Changes
+2. **Check Store Page**: Ensure the Store page exists and has `[woonoow_spa]`
+3. **Clear Cache**: Purge all caching layers
+
+### Blank Pages After Enabling
+
+1. Verify SPA Mode is set to "Full"
+2. Clear browser cache
+3. Check for JavaScript errors in browser console
+
+### Want to Test Before Enabling
+
+1. Keep mode as "Disabled"
+2. Visit `/store/` directly to preview SPA
+3. Switch to "Full" when satisfied