Relax minimum Go version requirement

[abhinavgautam01]

closes #64
##Summary

• lower Go version in go.mod to 1.25.6 to match dependency minimums
• pin Gitea SDK to v0.23.2 (last series requiring Go 1.23) to avoid forcing Go 1.26
• update Gitea merge/secret calls for the older SDK API

##Testing

• go build -v ./...
• go test -v -race ./...
• go tool golangci-lint run ./...

[untitaker]

I really do not think downgrading gitea SDK is acceptable cost for supporting older go versions.

[andrew]

I agree, I don’t think it’s worth the rollback