Clean up typos in docs, comments, and UI copy (#6045)

# Description of Changes

Fix wording, numbering, path references, and minor grammar issues across
project guides, backend comments, and frontend strings.

This keeps documentation and user-facing text consistent without
changing application behavior.

---

## Checklist

### General

- [x] 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)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### 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>

DeveloperGuide.md

@@ -92,7 +92,7 @@ Visit the [Lombok website](https://projectlombok.org/setup/) for installation in
 
 5. 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.
-5. **Frontend Setup (Required for Stirling 2.0)**
+6. **Frontend Setup (Required for Stirling 2.0)**
    Navigate to the frontend directory and install dependencies using npm.
 
 ### Verify Setup
@@ -275,7 +275,7 @@ Stirling-PDF uses different Docker images for various configurations. The build
 1. Set the security environment variable:
 
    ```bash
-   export DISABLE_ADDITIONAL_FEATURES=true  # or false for to enable login and security features for builds
+   export DISABLE_ADDITIONAL_FEATURES=true  # or false to enable login and security features for builds
    ```
 
 2. Build the project:
@@ -305,7 +305,7 @@ Stirling-PDF uses different Docker images for various configurations. The build
    docker build --no-cache --pull --build-arg VERSION_TAG=alpha -t stirlingtools/stirling-pdf:latest-fat -f ./Dockerfile.fat .
    ```
 
-Note: The `--no-cache` and `--pull` flags ensure that the build process uses the latest base images and doesn't use cached layers, which is useful for testing and ensuring reproducible builds. however to improve build times these can often be removed depending on your usecase
+Note: The `--no-cache` and `--pull` flags ensure that the build process uses the latest base images and doesn't use cached layers, which is useful for testing and ensuring reproducible builds. However, to improve build times these can often be removed depending on your use case
 
 ## 7. Testing