[khvn26]

Runs the Flagsmith SDK behavioural spec against this SDK on every pull request and push to main.

• sdk-spec/Steps.java: the steps file. It has one static method per SDK step, each marked with the Gherkin step text as a comment. It holds only SDK calls and the mapping to the spec's flag shape, so it doubles as a working usage example:

  // When the application gets the environment flags
  static List<SpecFlag> getEnvironmentFlags(FlagsmithClient flagsmith)
      throws FlagsmithClientError {
    return asSpecFlags(flagsmith.getEnvironmentFlags());
  }

• sdk-spec/Dockerfile: builds the SDK from source with Maven, then compiles the steps file together with the spec's Java harness, which comes from the harness build context. The harness finds the marked methods and runs them for the runner over stdin and stdout. No build file is needed in sdk-spec/, and nothing outside src/ is part of the published artefacts.

• .github/workflows/sdk-spec.yml: calls the spec's reusable workflow with language: java. It is pinned to v0.3.0.

• renovate.json: bumps the uses: ref and spec-ref together.

The spec currently covers getting environment flags and getting identity flags with traits.