feat: make /imkerei and /herkunft hero images admin-editable

Both pages are the ones most directly meant to give customers "ein
gutes Bild von der Imkerei" (per the active /goal), but their hero
images were still hardcoded PlaceholderImage tiles with no way to
ever swap in a real photo — unlike every homepage section, which
already went through this exact upload flow.

Added imkerei.image / herkunft.image to the content registry (new
"pages" group, since neither belongs under "Homepage") and switched
both pages from PlaceholderImage to ContentImage + getContentValue,
the same pattern already proven on the homepage sections. Falls back
to the identical placeholder tile until a photo is uploaded, so this
is a pure addition with no visual change until the owner uploads one.

Verified: tsc clean, 151/151 tests pass, both pages still render
correctly (curl 200 + screenshot) with the placeholder fallback.
Could not verify the admin upload UI end-to-end live — the local
admin account has 2FA enabled and I don't have the second factor;
confidence instead comes from reusing the identical, already-verified
AdminImageField/ContentImage wiring used for the four home.*.image
fields, plus generic (group-agnostic) admin field loading confirmed
by reading admin/inhalte/page.tsx.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

src/i18n/dictionary-type.ts

@@ -813,6 +813,7 @@ export interface Dictionary {
     intro: string;
     groupCompany: string;
     groupHome: string;
+    groupPages: string;
     groupLegal: string;
     groupSocial: string;
     deLabel: string;