Update help docs and AI knowledge base for SMS notifications

- Settings help article: add SMS Notifications subsection covering company opt-in, TCPA terms agreement, compose-before-send vs auto-send, and STOP opt-out
- Customers help article: add Mobile Phone and SMS Opt-In fields to the Adding a Customer field list
- HelpKnowledgeBase: remove stale "ready for pickup" SMS event, add company opt-in flow, customer opt-in requirement, compose modal for Admin/Manager, auto-send for ShopFloor, Send SMS button, and STOP opt-out behavior; remove SuperAdmin-only SMS Platform Setting content

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Views/Help/Customers.cshtml

@@ -89,6 +89,8 @@
                         <li><strong>Contact Name</strong> — the person you deal with day to day.</li>
                         <li><strong>Email</strong> — used for quote and invoice notifications.</li>
                         <li><strong>Phone</strong> — primary contact number.</li>
+                        <li><strong>Mobile Phone</strong> — used for SMS notifications. Required if you want to text this customer.</li>
+                        <li><strong>SMS Opt-In</strong> — check this only after you have obtained the customer's consent to receive text messages. Visible only when SMS is enabled for your company.</li>
                         <li><strong>Address</strong> — billing and shipping address fields.</li>
                     </ul>
                 </li>