Adds Messenger.send_error across the Discord (red embed with screenshot attached)
and generic (text-only) APIs. Bot._save_error_screenshot now also pushes the
failure to the configured messenger after saving the screenshot to disk, so each
approach/battle/exception failure is reviewable in Discord with the visual.
Gated by new config discord_log_errors ([general], default 1) and the
[discord_events] error toggle. Both optional/backward-compatible. Verified wiring
and the suppression path via a stubbed messenger.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
