Add SMS quote approval, fix Twilio credentials, fix passkey post-login redirect

- Add 'Send Quote via SMS' button on quote details page that sends the approval
  link to the customer via SMS (respects NotifyBySms, handles prospects via ProspectPhone)
- Reuses existing valid approval token rather than regenerating, so a previously
  emailed link stays valid when SMS is also sent
- Fix Twilio appsettings.json placeholders (real credentials moved to gitignored
  appsettings.Development.json)
- Fix passkey login ignoring ReturnUrl: biometric login on the login page now
  respects the form's ReturnUrl hidden field so QR-code and deep-link flows
  redirect correctly after authentication instead of always going to the dashboard

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

src/PowderCoating.Web/appsettings.json

@@ -48,9 +48,9 @@
     "FromName": "Powder Coating App Staff"
   },
   "Twilio": {
-    "AccountSid": "SK45bb87a7645d34c9227ea20faccad642",
-    "AuthToken": " f262409674753f285b1c8184785c270e",
-    "FromNumber": "+18664883595",
+    "AccountSid": "your-twilio-account-sid",
+    "AuthToken": "your-twilio-auth-token",
+    "FromNumber": "your-twilio-from-number",
     "DevRedirectPhone": ""
   },
   "Stripe": {