The generated code failed to compile if and endpoint had oauth2 enabled.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
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Summary by cubic

Fixes C++ Qt client OAuth2 code generation by removing scope/token redeclarations, using flow-suffixed variable names, and adopting a typed OauthMethod enum. Generated clients now compile and use clearer, safer auth flow handling.

• Bug Fixes
  • Use per-flow scope and token variables with descriptive names (e.g., scopeImplicitFlow, tokenAuthorizationFlow), set _latestScope per flow, and prevent collisions.
  • Replace magic ints with enum class OauthMethod across templates and samples (including tokenAvailable switches), and regenerate petstore samples.

^{Written for commit fef1373. Summary will update on new commits.}