feat(cms): white-label email templates and API doc config (#2)

## Summary

- Replace all hardcoded muellerprints brand identity in email templates with template variables sourced from env vars
- Inject shop context into both `sendInvoice` and `sendDeliveryNote` template calls in `order.ts`
- Make API documentation title/description env-var driven

## New env vars (all optional with safe defaults)

| Var | Default | Used in |
|-----|---------|---------|
| `SHOP_NAME` | `"Shop"` | Email subject, body, footer |
| `SHOP_CONTACT_NAME` | `""` | Email footer |
| `SHOP_ADDRESS` | `""` | Email footer |
| `SHOP_PHONE` | `""` | Email footer |
| `SHOP_EMAIL` | `ADMIN_EMAIL_ADDRESS` | Email footer |
| `SHOP_LOGO_URL` | `""` | Email header logo |
| `SHOP_SECONDARY_LOGO_URL` | `""` | Email footer logo |
| `API_TITLE` | `"Paperwork API"` | Swagger/OpenAPI title |
| `API_DESCRIPTION` | `"Paperwork API"` | Swagger/OpenAPI description |

## Test plan

- [ ] Set `SHOP_NAME=TestShop` and trigger invoice send → confirm subject and body use `TestShop`
- [ ] Leave `SHOP_NAME` unset → confirm default `"Shop"` appears
- [ ] Set `SHOP_LOGO_URL` → confirm logo renders in email header; unset → confirm no broken `<img>` tag
- [ ] Check Strapi admin `/documentation` with `API_TITLE=MyAPI` env var

Closes #1

Reviewed-on: #2
Co-authored-by: Michael Czechowski <mail@dailysh.it>
Co-committed-by: Michael Czechowski <mail@dailysh.it>

src/extensions/documentation/config/settings.json

@@ -2,8 +2,8 @@
 	"openapi": "3.0.1",
 	"info": {
 		"version": "1.0.0",
-		"title": "MUELLERPTINTS. Paperwork",
-		"description": "API Documentation for MUELLERPRINTS. Paperwork",
+		"title": "Paperwork API",
+		"description": "Paperwork API",
 		"termsOfService": false,
 		"contact": false,
 		"license": false