Make the collected app metadata available as an API

### Problem to solve

The app's metadata is publicly available but not standardized, so it can change at any time and affect compatibility.

### Proposal

Create a more stable, standardized endpoint, possibly with versioning. Consider creating multiple versions of the data: one resulting from crawling a source, and another that is more internal and tailored to the app’s requirements.

How does it work with attribution? #231

Maybe support LLMs or support multiple formats like csv, ...

### Links / references / screenshots

- #231
- #278
- https://www.useosm.org/resources, https://github.com/unpatterned-labs/useosm
- https://5stardata.info/de/

No files, tests, or entry points are named. Start by locating how app metadata is currently collected and exposed, then review issues #231 and #278 and the linked references. Done means an agreed, standardized and versioned API design covering source variants, formats, and attribution.

Written by the indexing model from the issue text.