style: Adjust default context lines and Markdown spacing

This commit applies final readability adjustments to the output of
`scripts/gha/get_pr_review_comments.py`:

- The default value for the `--context-lines` argument has been
  changed from 10 to 0. This means the full diff hunk will be
  displayed by default, aligning with your feedback preferring
  more context initially unless otherwise specified. The help text
  for this argument has also been updated.
- Markdown Spacing:
    - An additional newline is added after the main H1 title
      ("# Review Comments") for better separation.
    - A newline is added before the "### Context:" H3 subheading
      to separate it from the metadata list.
    - A newline is added before the "### Comment:" H3 subheading
      to separate it from the diff hunk block.

These changes further refine the script's output for clarity and
your experience.

Author: google-labs-jules[bot]

scripts/gha/get_pr_review_comments.py

@@ -66,9 +66,9 @@ def main():
     parser.add_argument(
         "--context-lines",
         type=int,
-        default=10,
+        default=0,
         help="Number of context lines from the diff hunk. Use 0 for the full hunk. "
-             "If > 0, shows the last N lines of the hunk. Default: 10."
+             "If > 0, shows the last N lines of the hunk. Default: 0."
     )
     parser.add_argument(
         "--since",
@@ -113,7 +113,7 @@ def main():
         return
 
     latest_created_at_obj = None
-    print("# Review Comments\n")
+    print("# Review Comments\n\n")
     for comment in comments:
         created_at_str = comment.get("created_at")
 
@@ -179,7 +179,7 @@ def main():
         print(f"*   **Line**: `{line_to_display}`") # Label changed from "Line in File Diff"
         print(f"*   **URL**: <{html_url}>\n")
 
-        print("### Context:")
+        print("\n### Context:")
         print("```") # Start of Markdown code block
         if diff_hunk and diff_hunk.strip():
             hunk_lines = diff_hunk.split('\n')
@@ -194,7 +194,7 @@ def main():
             print("(No diff hunk available for this comment)")
         print("```") # End of Markdown code block
 
-        print("### Comment:")
+        print("\n### Comment:")
         print(body)
         print("\n---")