V1 merge (#5193)

# Description of Changes

<!--
Please provide a summary of the changes, including:

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

Closes #(issue_number)
-->

---

## 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.

---------

Signed-off-by: dependabot[bot] <support@github.com>
Signed-off-by: Balázs Szücs <bszucs1209@gmail.com>
Signed-off-by: stirlingbot[bot] <stirlingbot[bot]@users.noreply.github.com>
Co-authored-by: ConnorYoh <40631091+ConnorYoh@users.noreply.github.com>
Co-authored-by: Connor Yoh <connor@stirlingpdf.com>
Co-authored-by: OUNZAR Aymane <aymane.ounzar@imt-atlantique.net>
Co-authored-by: YAOU Reda <yaoureda24@gmail.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: stirlingbot[bot] <195170888+stirlingbot[bot]@users.noreply.github.com>
Co-authored-by: Balázs Szücs <127139797+balazs-szucs@users.noreply.github.com>
Co-authored-by: Ludy <Ludy87@users.noreply.github.com>
Co-authored-by: tkymmm <136296842+tkymmm@users.noreply.github.com>
Co-authored-by: Peter Dave Hello <hsu@peterdavehello.org>
Co-authored-by: albanobattistella <34811668+albanobattistella@users.noreply.github.com>
Co-authored-by: PingLin8888 <88387490+PingLin8888@users.noreply.github.com>
Co-authored-by: FdaSilvaYY <FdaSilvaYY@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: OteJlo <106060728+OteJlo@users.noreply.github.com>
Co-authored-by: Angel <41905618+TheShadowAngel@users.noreply.github.com>
Co-authored-by: Ricardo Catarino <ricardomicc@gmail.com>
Co-authored-by: Luis Antonio Argüelles González <luis.arguelles@encora.com>
Co-authored-by: Dawid Urbański <31166488+urbaned121@users.noreply.github.com>
Co-authored-by: Stephan Paternotte <Stephan-P@users.noreply.github.com>
Co-authored-by: Leonardo Santos Paulucio <leonardo.paulucio@hotmail.com>
Co-authored-by: hamza khalem <72972114+hamzakhalem@users.noreply.github.com>
Co-authored-by: IT Creativity + Art Team <admin@it-playground.net>
Co-authored-by: Reece Browne <74901996+reecebrowne@users.noreply.github.com>
Co-authored-by: James Brunton <jbrunton96@gmail.com>
Co-authored-by: Victor Villarreal <133383186+vvillarreal-cfee@users.noreply.github.com>

devGuide/DeveloperGuide.md

@@ -12,6 +12,7 @@ Stirling-PDF is built using:
 - PDFBox
 - LibreOffice
 - qpdf
+- Calibre (`ebook-convert` CLI) for eBook conversions
 - HTML, CSS, JavaScript
 - Docker
 - PDF.js
@@ -54,7 +55,12 @@ Stirling-PDF is built using:
 Stirling-PDF uses Lombok to reduce boilerplate code. Some IDEs, like Eclipse, don't support Lombok out of the box. To set up Lombok in your development environment:
 Visit the [Lombok website](https://projectlombok.org/setup/) for installation instructions specific to your IDE.
 
-5. Add environment variable
+5. Install Calibre CLI (optional but required for eBook conversions)
+   Ensure the `ebook-convert` binary from Calibre is available on your PATH when working on the
+   eBook to PDF feature. The Calibre tool group is automatically disabled when the binary is
+   missing, so having it installed locally allows you to exercise the full workflow.
+
+6. Add environment variable
 For local testing, you should generally be testing the full 'Security' version of Stirling PDF. To do this, you must add the environment flag DISABLE_ADDITIONAL_FEATURES=false to your system and/or IDE build/run step.
 
 ## 4. Project Structure