fix(ui): correct CSS visibility typo; clean up spelling/grammar across codebase (#4661)

# Description of Changes

**What was changed**
- Fixed a CSS typo in `imageHighlighter.css` (`visbility` →
`visibility`) to restore the intended transition behavior.
- Corrected spelling/grammar in logs, comments, and console messages:
  - `PdfUtils.java`: log message “overlayed” → “overlaid”.
  - `CustomPDFDocumentFactoryTest.java`: comment typo “neeed” → “need”.
  - `FlattenController.java`: comment “readd” → “re-add”.
  - `PdfContainer.js`: console log “Hidding” → “Hiding”.
  - `navbar.js`: clarified tooltip comment wording.
  - `languages.html`: corrected Vietnamese label to “Tiếng Việt”.
- `ConvertWebsiteToPdfTest.java`: converted/de-duplicated comments to
clear English and improved assertion messages.
- No functional code paths altered except the CSS fix; the rest are
non-functional text improvements (logs/comments/tests/labels).

**Why the change was made**
- The CSS typo prevented the `visibility` transition from working as
intended.
- Consistent, correct wording improves developer experience, test
readability, and UI polish (language list).

---

## 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 <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Reece Browne <74901996+reecebrowne@users.noreply.github.com>

app/common/src/main/java/stirling/software/common/util/PdfUtils.java

@@ -567,7 +567,7 @@ public class PdfUtils {
                 PDImageXObject image = PDImageXObject.createFromByteArray(document, imageBytes, "");
                 // Draw the image onto the page at the specified x and y coordinates
                 contentStream.drawImage(image, x, y);
-                log.info("Image successfully overlayed onto PDF");
+                log.info("Image successfully overlaid onto PDF");
                 if (!everyPage && i == 0) {
                     break;
                 }