Diff viewer doesn't clearly indicate when an entirely new file is created

[Randalphwa]

When running code generation verification (--verify_cpp), the log file reports "Updated: filename" for both modified files and newly created files. The diff viewer needs to clearly distinguish between:

1. Files that were modified (existing file with changes)
2. Files that were newly created (didn't exist before)

Expected behavior: The log should show something like:

• Created: path/to/new/file.h for new files
• Updated: path/to/existing/file.h for modified files

Current behavior: Both cases show Updated: path/to/file.h, making it unclear when a file is entirely new vs. modified.

Impact: This makes it difficult to understand what changed during code generation verification, especially when debugging generation issues or reviewing changes.