Fix schema generator path resolution to be independent of working directory

[aliok]

Introduced here: #155 (comment)

Problem

The schema generator in hack/jsonschemagen/main.go uses filepath.Join("..", "..", "specs") to build the output path for schema files. This approach only works when the binary is executed from the hack/jsonschemagen directory. When run from the repository root (as done by make update-codegen and CI workflows with go run ./hack/jsonschemagen), this resolves to an incorrect path (../../specs from repo root) and causes the write operation to fail.

Impact

• Schema generation fails when invoked from the repo root
• CI workflows and make targets cannot successfully generate schemas
• Inconsistent behavior depending on the current working directory

Proposed Solution

Use runtime.Caller to determine the source file's location, then derive the repository root from there before appending specs. This makes the path resolution independent of the current working directory:

_, callerFile, _, ok := runtime.Caller(0)
if !ok {
    log.Fatal("failed to determine generator location")
}
repoRoot := filepath.Join(filepath.Dir(callerFile), "..", "..")
specsDir := filepath.Join(repoRoot, "specs")