Remove backend UI (#4023)

# Description of Changes

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Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
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---

## 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: Copilot <[email protected]>

app/core/src/main/resources/application.properties

@@ -25,7 +25,7 @@ server.servlet.context-path=${SYSTEM_ROOTURIPATH:/}
 spring.devtools.restart.enabled=true
 spring.devtools.livereload.enabled=true
 spring.devtools.restart.exclude=stirling.software.proprietary.security/**
-spring.thymeleaf.encoding=UTF-8
+# spring.thymeleaf.encoding=UTF-8 # Disabled - React frontend replaces Thymeleaf
 spring.web.resources.mime-mappings.webmanifest=application/manifest+json
 spring.mvc.async.request-timeout=${SYSTEM_CONNECTIONTIMEOUTMILLISECONDS:1200000}
 
@@ -35,6 +35,14 @@ spring.datasource.username=sa
 spring.datasource.password=
 spring.h2.console.enabled=false
 spring.jpa.hibernate.ddl-auto=update
+# Defer datasource initialization to ensure that the database is fully set up 
+# before Hibernate attempts to access it. This is particularly useful when 
+# using database initialization scripts or tools.
+spring.jpa.defer-datasource-initialization=true
+
+# Disable SQL logging to avoid cluttering the logs in production. Enable this 
+# property during development if you need to debug SQL queries.
+spring.jpa.show-sql=false
 server.servlet.session.timeout:30m
 # Change the default URL path for OpenAPI JSON
 springdoc.api-docs.path=/v1/api-docs