ci: add actionlint workflow gate

[Serph91P]

Summary

Adds an actionlint workflow gate to all .github/workflows/ files in this repository.

Verification

The workflow runs on:

• Pull requests targeting develop or main when workflow files change
• Pushes to develop or main when workflow files change
• Manual invocation via workflow_dispatch

It uses actionlint 1.7.12 to lint all workflow files and fails the PR if errors are found.

Links

• Repository: plugin.video.twitch
• Workflow file: .github/workflows/workflow-lint.yml
• Actionlint action: raven-actions/actionlint@3d39aea

[Serph91P]

Independent final review completed at exact head 21206cf6405bf68353c0f09f704db0aad4598018.

Checks performed:

• Reviewed the one-file diff against the recorded origin/develop base 76e3c9327b57b1dfd9c063c76457fd54778260e5.
• Ran actionlint 1.7.12 across all five workflow files with no findings.
• Parsed all five workflows with PyYAML and validated the repository workflow policy with no errors.
• Ran tests.test_workflow_validation: 103 tests passed.
• Confirmed immutable action pins, read-only permissions, develop/main path filters, explicit actionlint 1.7.12, clean diff checks, and no U+2013 or U+2014.
• Confirmed all nine GitHub checks pass at this exact head, including Workflow Lint.

No blocking findings. This head is accepted for merge into develop.