Replace GITHUB_AUTH_HEADER with GH_TOKEN

[kevinbackhouse]

I think these tokens will always be the same, so there's no reason to have two separate environment variables.

[Copilot]

Pull request overview

This PR standardizes authentication configuration by removing the dedicated GITHUB_AUTH_HEADER environment variable and using GH_TOKEN (token-only) instead, with the Bearer prefix applied where needed.

Changes:

• Update the GitHub official toolbox to build the Authorization: Bearer … header from GH_TOKEN.
• Update developer/run documentation and the Docker run helper to reference GH_TOKEN.
• Update the smoketest workflow to pass GH_TOKEN (token-only) instead of a preformatted auth header.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/seclab_taskflow_agent/toolboxes/github_official.yaml	Switches Authorization header construction to Bearer {{ env('GH_TOKEN') }}.
docker/run.sh	Updates usage instructions to export GH_TOKEN instead of GITHUB_AUTH_HEADER.
README.md	Updates the toolbox configuration example to use GH_TOKEN with a Bearer prefix.
.github/workflows/smoketest.yaml	Passes GH_TOKEN (raw token) into the smoketest job environment.

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