feat: Improve team management UX with message-based feedback and internal team protection (#3719)

# Description of Changes

- Refactored team management logic to unify and streamline feedback via
`messageType` query parameters.
- Added backend checks to prevent renaming, deleting, or reassigning
users to/from the protected Internal team.
- Updated Thymeleaf templates (`teams.html`, `team-details.html`,
`adminSettings.html`) to support user-visible success and error messages
based on controller redirects.
- Ensured `team.cannotMoveInternalUsers`,
`team.internalTeamNotAccessible`, and `invalidRoleMessage` are properly
internationalized.
- Replaced hardcoded `/adminSettings` redirects with `/teams` for more
consistent UX.

**Why**: 
To provide admins with immediate, meaningful feedback during team
operations and to enforce data integrity around protected teams like
"Internal".

---

## 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)
- [ ] 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

- [ ] 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)

- [ ] 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.

---------

Co-authored-by: Copilot <[email protected]>

stirling-pdf/src/main/resources/messages_en_GB.properties

@@ -200,6 +200,7 @@ disabledCurrentUserMessage=The current user cannot be disabled
 downgradeCurrentUserLongMessage=Cannot downgrade current user's role. Hence, current user will not be shown.
 userAlreadyExistsOAuthMessage=The user already exists as an OAuth2 user.
 userAlreadyExistsWebMessage=The user already exists as an web user.
+invalidRoleMessage=Invalid role.
 error=Error
 oops=Oops!
 help=Help

stirling-pdf/src/main/resources/templates/adminSettings.html

@@ -93,8 +93,8 @@
                   <span class="material-symbols-rounded">person_add</span>
                   <span th:text="#{adminUserSettings.addUser}">Add New User</span>
                 </button>
-                
-                <a href="/teams" class="data-btn data-btn-secondary" th:title="#{adminUserSettings.teams}">
+
+                <a th:href="@{'/teams'}" class="data-btn data-btn-secondary" th:title="#{adminUserSettings.teams}">
                   <span class="material-symbols-rounded">group</span>
                   <span th:text="#{adminUserSettings.teams}">Manage Teams</span>
                 </a>
@@ -108,7 +108,7 @@
                   <span th:text="#{adminUserSettings.changeUserRole}">Change User's Role</span>
                 </button>
                 
-                <a href="/usage" th:if="${@runningEE}" class="data-btn data-btn-secondary" th:title="#{adminUserSettings.usage}">
+                <a th:href="@{'/usage'}" th:if="${@runningEE}" class="data-btn data-btn-secondary" th:title="#{adminUserSettings.usage}">
                   <span class="material-symbols-rounded">analytics</span>
                   <span th:text="#{adminUserSettings.usage}">Usage Statistics</span>
                 </a>
@@ -120,27 +120,27 @@
                   <thead>
                     <tr>
                       <th scope="col">#</th>
-                      <th scope="col" th:title="#{username}" th:text="#{username}">Username</th>
-                      <th scope="col" th:title="#{adminUserSettings.team}" th:text="#{adminUserSettings.team}">Team</th>
-                      <th scope="col" th:title="#{adminUserSettings.role}" th:text="#{adminUserSettings.role}">Roles</th>
+                      <th scope="col" th:title="#{username}" class="text-overflow" th:text="#{username}">Username</th>
+                      <th scope="col" th:title="#{adminUserSettings.team}" class="text-overflow" th:text="#{adminUserSettings.team}">Team</th>
+                      <th scope="col" th:title="#{adminUserSettings.role}" class="text-overflow" th:text="#{adminUserSettings.role}">Roles</th>
                       <th scope="col" th:title="#{adminUserSettings.authenticated}" class="text-overflow" th:text="#{adminUserSettings.authenticated}">Authenticated</th>
                       <th scope="col" th:title="#{adminUserSettings.lastRequest}" class="text-overflow" th:text="#{adminUserSettings.lastRequest}">Last Request</th>
-                      <th scope="col" th:title="#{adminUserSettings.actions}" th:text="#{adminUserSettings.actions}">Actions</th>
+                      <th scope="col" th:title="#{adminUserSettings.actions}" class="text-overflow" th:text="#{adminUserSettings.actions}">Actions</th>
                     </tr>
                   </thead>
                   <tbody>
                     <tr th:each="user : ${users}">
-                      <td th:text="${user.id}"></td>
-                      <td th:text="${user.username}" th:classappend="${userSessions[user.username] ? 'active-user' : ''}"></td>
-                      <td th:text="${user.team != null ? user.team.name : '—'}"></td>
+                      <td th:text="${user.id}" th:title="${user.id}" class="text-overflow"></td>
+                      <td th:text="${user.username}" th:title="${user.username}" class="text-overflow" th:classappend="${userSessions[user.username] ? 'active-user' : ''}"></td>
+                      <td th:text="${user.team != null ? user.team.name : '—'}" th:title="${user.team != null ? user.team.name : '—'}" class="text-overflow"></td>
                       <td>
                         <span class="data-badge" style="background-color: var(--md-sys-color-secondary-container); color: var(--md-sys-color-secondary); padding: 0.25rem 0.5rem; border-radius: 1rem; font-size: 0.875rem; display: inline-flex; align-items: center; gap: 0.25rem;">
                           <span class="material-symbols-rounded" style="font-size: 1rem;">shield</span>
-                          <span th:text="#{${user.roleName}}">Role</span>
+                          <span th:text="#{${user.roleName}}" th:title="#{${user.roleName}}" class="text-overflow">Role</span>
                         </span>
                       </td>
-                      <td th:text="${user.authenticationType}"></td>
-                      <td th:text="${userLastRequest[user.username] != null ? #dates.format(userLastRequest[user.username], 'yyyy-MM-dd HH:mm:ss') : 'N/A'}"></td>
+                      <td th:text="${user.authenticationType}" th:title="${user.authenticationType}"></td>
+                      <td th:text="${userLastRequest[user.username] != null ? #dates.format(userLastRequest[user.username], 'yyyy-MM-dd HH:mm:ss') : 'N/A'}" th:title="${userLastRequest[user.username] != null ? #dates.format(userLastRequest[user.username], 'yyyy-MM-dd HH:mm:ss') : 'N/A'}"></td>
                       <td>
                         <div class="data-action-cell">
                           <form th:if="${user.username != currentUsername}" th:action="@{'/api/v1/user/admin/deleteUser/' + ${user.username}}" method="post" onsubmit="return confirmDeleteUser()" style="display: inline;">