fix(terms): erase generated terms via the correct flag option key

[bordoni]

Fixes #219

Problem

The "Erase faked data" tool did not delete generated Categories (or any terms); all other faked data was removed correctly.

Root cause

Term generation flags terms in the option fakerpress.module_flag.terms (plural, via get_slug()):

update_option( 'fakerpress.module_flag.' . $this::get_slug(), $flagged ); // ...terms

But fetch() and delete() hard-coded the singular key:

public static function fetch( array $args = [] ): array {
    return get_option( 'fakerpress.module_flag.term', [] ); // singular -> always []
}

So the erase routine always received an empty set and never called wp_delete_term().

Fix

Align fetch()/delete() to the same get_slug()-based key that generation writes. Terms generated before the fix were stored under the plural key, so they are now correctly picked up.

Tests

TermEraseTest covers the flag → fetch → delete cycle: fetch() returns the flagged terms, and delete() removes both a category and a tag and clears the flag option.

Milestone: 0.9.2