[Audit][P3] Remove duplicate and dead theme/plugin code

## Context

The custom plugin bootstrap is disabled while duplicate widget implementations live in the theme. Templates also contain redundant bootstrapping and an unused unregistered setting.

Audit findings: 41 through 43.

## Scope

- Decide whether Academy Africa widgets belong to the theme or plugin and keep one source of truth.
- Remove redundant `wp-load.php` template includes.
- Remove or register the unused `slack_url` setting.

## Done when

- Widget ownership and activation behavior are documented and tested.
- Duplicate or dead implementations are removed safely.
- Templates rely on the normal WordPress bootstrap lifecycle.