KnowError Handler
Captures fatal PHP errors, logs them in WP-Admin, emails admins, and replaces the default WordPress critical-error page.
- Catches PHP fatal errors via `register_shutdown_function`.
- Logs every captured error to a database table (`{prefix}knowhalim_eh_errors`) so you never miss an error even if the email fails.
- Admin UI with two tabs: Settings and Errors (browseable list with detail view, mark read/unread, delete).
- Top-level admin menu with a red unread-count badge — same style as the Comments awaiting-moderation bubble.
- Restricted to administrators (`manage_options`) so other roles can't see error internals.
- Emails one or more recipients with full error context.
- Throttles duplicate emails for the same error fingerprint (logging is not throttled).
- Replaces the default "There has been a critical error on this website" message with custom HTML, OR redirects visitors to another page.