Add SMS Agreements admin page and update help docs

- Add /SmsAgreements SuperAdmin page listing per-company SMS terms acceptance
  status, with stats cards, filter/search, and a full acceptance history modal
  (terms version, accepted by, timestamp, IP, user agent)
- Add SMS Agreements nav link under Tenants & Billing in the platform sidebar
- Update HelpKnowledgeBase and Help docs (Quotes, Settings) to document
  quote approval via SMS and the reuse of existing approval tokens

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

src/PowderCoating.Web/Helpers/HelpKnowledgeBase.cs

@@ -1083,6 +1083,10 @@ public static class HelpKnowledgeBase
 
         **What events send an SMS:**
         - Job completed — notifies the customer their job is done and ready for pickup.
+        - Quote approval request — sends the customer a link to review and approve or decline their quote.
+
+        **Sending a quote approval link via SMS:**
+        On any quote's Details page, click **Send Quote via SMS**. The system texts the customer's mobile number a short message with the approval link. If no valid approval token exists yet, one is generated automatically. If an email was already sent for the same quote, the existing token is reused so both the email link and the SMS link remain valid simultaneously. The customer follows the link to the self-service approval portal and can approve or decline from their phone. Prospects (non-customers) receive the SMS at their ProspectPhone number without requiring an opt-in check; registered customers must have SMS Opt-In enabled.
 
         **Compose-before-send (Admin/Manager):**
         When a Company Admin or Manager marks a job complete, the system pre-fills an SMS draft based on your notification template and opens a compose modal before sending. You can personalize the message on the spot. The message must contain "STOP" opt-out language — it is appended automatically if missing.