Fuzzing tests

### OpenSSF Scorecard finding: Fuzzing

Add Go fuzz targets using testing.F for input-parsing logic (e.g. dependency version parsing, webhook payload handling). OSS-Fuzz integration gets full credit; native Go fuzzing in CI gets partial credit. 

### References:

- https://github.com/ossf/scorecard/blob/c22063e786c11f9dd714d777a687ff7c4599b600/docs/checks.md#fuzzing