fix: apply child theme config recursively after providers register

[rivanuff]

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[rivanuff]

Closing: the recursive merge and the deferral both turn out to have org-wide impact.

Audited all 57 repos requiring yard/nutshell. 18 have a child theme overriding a parent config key (250 file pairs). Of those, 26 pairs across 11 repos change substantively:

• user-roles.roles: +16 roles (kngf.nl/kwaliteitshuis), +15 (kngf.nl/richtlijnen), +1 (roosendaal/participatieeiland)
• yard-data.post_types: +6/+6/+5/+2 (kngf.nl x2, meppel, cultuurparticipatie)
• view.composers: +2 (roosendaal/participatieeiland), +1 (wilderszijde/leefstijl)
• console.commands: +1 (moerdijk/werkenbij, odu/ndc)
• poet.block_pattern_category: +1 (roosendaal x4, wilderszijde)
• yard-schema.credentials: +6/+7 (beeckestijn x2)
• facetwp.templates: numeric keys 0-3 merged into a named map (kngf.nl/richtlijnen)

Separately, the deferral breaks child app.providers: RegisterProviders reads config('app.providers') at bootstrapper #5, the deferred callback runs at #6. gorinchem/werkenbij, roosendaal/participatieeiland and wilderszijde/leefstijl define providers in the child theme; wilderszijde would silently lose GoogleFontsServiceProvider.

Moving the fix into package-meedoen instead, scoped to its own config key.