SSO Refactoring (#2818)

# Description of Changes

* Refactoring of SSO code around OAuth & SAML 2
* Enabling auto-login with SAML 2 via the new `SSOAutoLogin` property
* Correcting typos & general cleanup

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [x] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [x] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [x] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

src/main/resources/templates/account.html

@@ -34,7 +34,7 @@
               </th:block>
 
               <!-- Change Username Form -->
-              <th:block th:if="${!oAuth2Login}">
+              <th:block th:if="not ${oAuth2Login} or not ${saml2Login}">
               <h4 th:text="#{account.changeUsername}">Change Username?</h4>
               <form id="formsavechangeusername" class="bg-card mt-4 mb-4" th:action="@{'/api/v1/user/change-username'}" method="post">
                 <div class="mb-3">
@@ -53,7 +53,7 @@
               </th:block>
 
               <!-- Change Password Form -->
-              <th:block th:if="${!oAuth2Login}">
+              <th:block th:if="not ${oAuth2Login} or not ${saml2Login}">
               <h4 th:text="#{account.changePassword}">Change Password?</h4>
               <form id="formsavechangepassword" class="bg-card mt-4 mb-4" th:action="@{'/api/v1/user/change-password'}" method="post">
                 <div class="mb-3">