feat: add annotation option to PDF to image (#4365)

## Summary
- add optional flag to include PDF annotations when converting to images
- expose annotation option via API model and UI checkbox
- add translation for annotation option

## Testing
- `./gradlew spotlessApply`
- `./gradlew build`


------
https://chatgpt.com/codex/tasks/task_b_68b7fa1d5a1c83288342244a0ec85e9d

app/core/src/main/resources/messages_en_GB.properties

@@ -1439,6 +1439,7 @@ pdfToImage.dpi=DPI (The server limit is {0} dpi)
 pdfToImage.submit=Convert
 pdfToImage.info=Python is not installed. Required for WebP conversion.
 pdfToImage.placeholder=(e.g. 1,2,8 or 4,7,12-16 or 2n-1)
+pdfToImage.includeAnnotations=Include annotations (comments, highlights etc.)
 
 
 #addPassword

app/core/src/main/resources/templates/convert/pdf-to-img.html

@@ -73,6 +73,10 @@
                   <option value="blackwhite" th:text="#{pdfToImage.blackwhite}"></option>
                 </select>
               </div>
+              <div class="mb-3 form-check">
+                <input class="form-check-input" type="checkbox" id="includeAnnotations" name="includeAnnotations">
+                <label class="form-check-label" for="includeAnnotations" th:text="#{pdfToImage.includeAnnotations}"></label>
+              </div>
               <div class="mb-3">
                 <label for="dpi">DPI:</label>
                 <input type="number" name="dpi" class="form-control" id="dpi" min="1" step="1" value="300" required>