Stop reporting external feed-source errors to Honeybadger

[dreikanter]

Summary

• External feed-source failures (broken TLS, network errors, non-2xx responses) were being reported to Honeybadger on every pull, even though they are not code bugs and are already tracked locally in the errors table and per-feed counters. One dead source (commitstrip, failing its TLS handshake) generated 125 notices in 11 days — pure recurring noise that buries real bugs.
• Added a notify: option to ErrorDumper (default true). When false, it skips Honeybadger.notify but still persists the Error record, so local visibility is unchanged.
• ProcessFeed now classifies HTTP::Error, OpenSSL::SSL::SSLError, and HttpLoader::Error as source errors and dumps them with notify: false. Genuinely unexpected errors (parser bugs, NoMethodError, etc.) still report to Honeybadger.
• Added OpenSSL::SSL::SSLError to HttpClient retryable errors so a transient handshake blip gets one retry, like timeouts and connection errors.

Checklist

• Updated CHANGELOG.md under Unreleased, or change is internal-only