V1 merge (#5193)

# 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

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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.

---------

Signed-off-by: dependabot[bot] <[email protected]>
Signed-off-by: Balázs Szücs <[email protected]>
Signed-off-by: stirlingbot[bot] <stirlingbot[bot]@users.noreply.github.com>
Co-authored-by: ConnorYoh <[email protected]>
Co-authored-by: Connor Yoh <[email protected]>
Co-authored-by: OUNZAR Aymane <[email protected]>
Co-authored-by: YAOU Reda <[email protected]>
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 <[email protected]>
Co-authored-by: Ludy <[email protected]>
Co-authored-by: tkymmm <[email protected]>
Co-authored-by: Peter Dave Hello <[email protected]>
Co-authored-by: albanobattistella <[email protected]>
Co-authored-by: PingLin8888 <[email protected]>
Co-authored-by: FdaSilvaYY <[email protected]>
Co-authored-by: Copilot <[email protected]>
Co-authored-by: OteJlo <[email protected]>
Co-authored-by: Angel <[email protected]>
Co-authored-by: Ricardo Catarino <[email protected]>
Co-authored-by: Luis Antonio Argüelles González <[email protected]>
Co-authored-by: Dawid Urbański <[email protected]>
Co-authored-by: Stephan Paternotte <[email protected]>
Co-authored-by: Leonardo Santos Paulucio <[email protected]>
Co-authored-by: hamza khalem <[email protected]>
Co-authored-by: IT Creativity + Art Team <[email protected]>
Co-authored-by: Reece Browne <[email protected]>
Co-authored-by: James Brunton <[email protected]>
Co-authored-by: Victor Villarreal <[email protected]>

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