chore: use custom GitHub App for update PRs so tests can run

[maakle]

Note

Medium Risk
Changes CI authentication/permissions and workflow execution path; misconfiguration of app secrets or token scopes could break SDK generation or PR creation.

Overview
Updates the SDK Generation GitHub Actions workflow to run SDK generation directly in the job (rather than calling the shared workflow-executor reusable workflow), including a new always-on step to log generation results.

Switches authentication from GITHUB_TOKEN/explicit workflow permissions to a GitHub App token (actions/create-github-app-token) so generated PRs can trigger downstream workflows (e.g., test suite), while keeping the same dispatch/scheduled triggers and kombo-python target.

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