Bug: CompareHeaders function fails to handle missing headers properly labels: bug, test-failure

The CompareHeaders function currently fails to properly handle and display differences when expected headers are missing from the actual headers map.

Current Behavior
When an expected header is missing from the actual headers:

The test fails with error: "CompareHeaders() didn't properly show missing Authorization header"
The diff output doesn't properly highlight or indicate the missing header
The function may panic or produce incorrect output when trying to process missing values

Expected Behavior
When comparing headers and encountering missing values, the function should:

Clearly indicate which headers are missing in the actual headers
Mark missing headers appropriately in the diff visualization

The fails for
expected := map[string]string{
"Authorization": "Bearer token123",
"User-Agent": "test-client",
}
actual := map[string]string{
"User-Agent": "test-client",
}

Start by locating the CompareHeaders function and reproduce the issue with the expected and actual maps shown in the report. Done means a missing Authorization header is clearly identified in the diff without a panic or incorrect output.