Public provider catalogue endpoint for GeMeDa integrations

The GeMeDa portal currently keeps its metasearch provider list in frontend code. External clients such as the webtrees module need a stable, public source for the available provider identifiers and labels.

Please provide and document a public endpoint that returns the current provider catalogue, including:

• a stable technical provider ID;
• a display name;
• the existing metasearch ID where applicable;
• clear caching and update semantics.

The endpoint should not require an authentication key because it exposes only provider metadata. This avoids stale, duplicated provider lists in integrations.