style(spotless): centralize and expand formatting config in root build.gradle (#4098)

# Description of Changes

- Removed redundant `spotless` configurations from `app/common`,
`app/core`, and `app/proprietary` modules.
- Consolidated all formatting logic into the root `build.gradle` file.
- Extended Spotless support to include:
  - YAML files (`*.yml`, `*.yaml`)
  - Gradle scripts (`*.gradle`, including nested `app/**/*.gradle`)
- Updated `googleJavaFormatVersion` from `1.27.0` to `1.28.0`.

This change improves maintainability by enforcing consistent formatting
across all modules from a single location. Additionally, it ensures
formatting is applied to Gradle and YAML files, which were previously
unformatted.

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## 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/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)
- [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)
- [ ] 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.