`list projects` fails with "error decoding response body"

## What

`fossapi list projects` fails with a deserialization error against the
real `/api/projects` endpoint:

```
$ fossapi list projects --json --count 1
Error: HTTP error: error decoding response body
```

The same key works fine for `get project `, `get revision
`, and a direct `curl` against `/api/projects?count=1` returns
valid JSON — so the response itself is well-formed. Only fossapi's
response struct is intolerant of something in it.

## Suggested fix

- Make the response struct tolerant of unknown / nullable fields
(`#[serde(default)]`, `Option`).
- If repro is hard to set up, comparing the live `/api/projects` JSON
shape against the struct definition should surface the offending
field(s).