Add audit system, invite links, and usage analytics (#4749)

# Description of Changes

New Features
Audit System: Complete audit logging with dashboard, event tracking, and
export capabilities

Invite Links: Secure invite system with email notifications and
expiration

Usage Analytics: Endpoint usage statistics and visualization

License Management: User counting with grandfathering and license
enforcement
## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/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/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] 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)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/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/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: James Brunton <jbrunton96@gmail.com>

app/core/src/main/java/stirling/software/SPDF/controller/api/misc/ConfigController.java

@@ -62,8 +62,10 @@ public class ConfigController {
             // Security settings
             configData.put("enableLogin", applicationProperties.getSecurity().getEnableLogin());
 
-            // Mail settings
-            configData.put("enableEmailInvites", applicationProperties.getMail().isEnableInvites());
+            // Mail settings - check both SMTP enabled AND invites enabled
+            boolean smtpEnabled = applicationProperties.getMail().isEnabled();
+            boolean invitesEnabled = applicationProperties.getMail().isEnableInvites();
+            configData.put("enableEmailInvites", smtpEnabled && invitesEnabled);
 
             // Check if user is admin using UserServiceInterface
             boolean isAdmin = false;

app/core/src/main/resources/settings.yml.template

@@ -128,6 +128,7 @@ system:
   disableSanitize: false # set to true to disable Sanitize HTML; (can lead to injections in HTML)
   maxDPI: 500 # Maximum allowed DPI for PDF to image conversion
   corsAllowedOrigins: [] # List of allowed origins for CORS (e.g. ['http://localhost:5173', 'https://app.example.com']). Leave empty to disable CORS.
+  frontendUrl: '' # Base URL for frontend (e.g. 'https://pdf.example.com'). Used for generating invite links in emails. If empty, falls back to backend URL.
   serverCertificate:
     enabled: true # Enable server-side certificate for "Sign with Stirling-PDF" option
     organizationName: Stirling-PDF # Organization name for generated certificates