Support code suggestions in @gemini-cli /review (#66)

### Description
Enable GitHub PR suggestions in inline comments

### Approach
This PR tells the `@gemini-cli /review` agent to prefer GitHub
suggestions.

So instead of the model posting a comment like:
```
You should change this line to: <NEW CODE>
```

It should instead follow the format:
````
You should change this line to 
```suggestion
<NEW CODE>
```
````

### Testing
Ran this action on an example PR and see the suggestions (boxed for
convenience):
<img width="629" height="1270" alt="image"
src="https://github.com/user-attachments/assets/f67199e6-2c12-4fa8-82f8-b43356f30349"
/>

Author: leehagoodjames

.github/workflows/gemini-pr-review.yml

@@ -238,7 +238,11 @@ jobs:
                detailed review feedback here>")
             2. Posting the review:
                 2.1 Use the mcp__github__create_pending_pull_request_review to create a Pending Pull Request Review.
-                2.2 Use the mcp__github__add_comment_to_pending_review to add comments to the Pending Pull Request Review. Inline comments are preffered whenever possible, so repeat this step, calling mcp__github__add_comment_to_pending_review, as needed. All comments about specific lines of code should use inline comments.
+                2.2 Use the mcp__github__add_comment_to_pending_review to add comments to the Pending Pull Request Review. Inline comments are preffered whenever possible, so repeat this step, calling mcp__github__add_comment_to_pending_review, as needed. All comments about specific lines of code should use inline comments. It is preferred to use code suggestions when possible, which include a code block that is labeled "suggestion", which contains what the new code should be. An example is:
+                  {{COMMENT_TEXT}}
+                  ```suggestion
+                  {{CODE_SUGGESTION}}
+                  ```
                 2.3 Use the mcp__github__submit_pending_pull_request_review to submit the Pending Pull Request Review.
 
             Review Areas:

workflows/pr-review/gemini-pr-review.yml

@@ -238,7 +238,11 @@ jobs:
                detailed review feedback here>")
             2. Posting the review:
                 2.1 Use the mcp__github__create_pending_pull_request_review to create a Pending Pull Request Review.
-                2.2 Use the mcp__github__add_comment_to_pending_review to add comments to the Pending Pull Request Review. Inline comments are preffered whenever possible, so repeat this step, calling mcp__github__add_comment_to_pending_review, as needed. All comments about specific lines of code should use inline comments.
+                2.2 Use the mcp__github__add_comment_to_pending_review to add comments to the Pending Pull Request Review. Inline comments are preffered whenever possible, so repeat this step, calling mcp__github__add_comment_to_pending_review, as needed. All comments about specific lines of code should use inline comments. It is preferred to use code suggestions when possible, which include a code block that is labeled "suggestion", which contains what the new code should be. An example is:
+                  {{COMMENT_TEXT}}
+                  ```suggestion
+                  {{CODE_SUGGESTION}}
+                  ```
                 2.3 Use the mcp__github__submit_pending_pull_request_review to submit the Pending Pull Request Review.
 
             Review Areas: