Add HTTP Status Code column to CSV output

[ocervell]

What

Adds the HTTP response status code to EyeWitness's machine-readable output.

• security_headers.collect_http_headers already makes the request but discarded response.status on success. It now captures it (and e.code on HTTPError) into the collected headers as Response Code.
• reporting.py gains a Status Code column in Requests.csv (after Request Status), populated from that value.

Why

Requests.csv only exposed Request Status — the browser outcome (Successful / Timeout / BadStatus / …), not the actual HTTP code. Tools that consume the CSV had no way to distinguish a 200 from a 301/404/500 that still rendered. This surfaces the real code (relates to #141, whose "Response Code in headers" behavior had since been refactored out).

Behavior

• Successful responses now record the real code (e.g. 200, 301).
• HTTPError responses record the error code (e.g. 404, 500).
• Connection-level failures (timeout / refused / DNS / SSL) leave the column blank, as no HTTP response was received.
• The value is also injected into the headers section (Response Code), so it shows in the HTML report too.

Testing

Ran --web against a local nginx target:

Protocol,Port,Domain,URL,Resolved,Request Status,Status Code,Title,...
http,8082,127.0.0.1,http://127.0.0.1:8082,Unknown,Successful,200,"Welcome to nginx!",...