Many posts use the bare product logo or no image for link previews #245

Problem

The product Open Graph images (openam-og.png, opendj-og.png, openig-og.png, and openidm-og.png / openicf-og.png from #244) are 1024×512 cards made for link previews. Many posts do not use them.

1. Posts that use the bare product logo (28 posts)

imageurl: points at the ~700×172 logo strip instead of the OG card, so Facebook / X / LinkedIn previews show a thin, cropped logo:

(The 10 OpenICF posts that use openicf-logo.png are already switched in #244.)

2. Posts with no imageurl at all (27 posts)

header.html falls back to the GitHub organisation avatar for og:image / twitter:image, and the Pinterest button (#242) is not shown. 21 of them are about a specific product (e.g. 2024-03-15-openam-quick-start-guide, 2025-11-05-openig-getting-started, 2025-11-05-opendj-getting-started, OpenAM JEE agents and OpenIDM 7.0.1 / 7.1.0 release notes); 6 are general articles with no product (stateless-vs-stateful-authentication, adaptive-authentication, passwordless-authentication-methods, sso-seamless-authentication-enterprise-client-services, llm-in-access-management, how-to-auth-via-esia).

(The 3 OpenICF posts without imageurl are covered in #244, the redirect … copy.md is removed in #242, and the empty imageurl: '' is fixed in #239.)

3. Wrong title on the ESIA article

_posts/2019-07-31-how-to-auth-via-esia.md has the home page's landing-title: "Welcome to Open Identity Platform Community" (and landing-title2) copied into it; its real heading is # Аутентификация через госуслуги (ЕСИА). Once #239 is merged this wrong title also becomes the page <title>.

grep -h '^imageurl' _posts/* | sort | uniq -c
grep -L '^imageurl' _posts/*

Suggested fix

• Switch the 28 posts from *-logo.png to the matching *-og.png.
• Give the 21 product posts the OG image of their product (the first entry of products: for multi-product posts).
• Add a platform-wide oip-og.png in the same 1024×512 format, built from oip-star.png, and use it for the 6 general articles.
• Fix the ESIA article's title.

Depends on #244 for openidm-og.png.