fix: reject --include-repos/--exclude-repos with --repo in github scan

[kashifkhan0771]

Explicit --repo entries bypass org-scan filtering entirely, so combining with --include-repos/--exclude-repos silently ignored patterns instead of erroring. Add validation + doc comments explaining the bypass.

Description:

Explain the purpose of the PR.

Checklist:

• Tests passing (make test-community)?
• Lint passing (make lint this requires golangci-lint)?

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Note

Low Risk
Small CLI/config validation and documentation only; no change to GitHub enumeration or scanning behavior when flags are used correctly.

Overview
GitHub scans now fail fast when --repo is used together with --include-repos or --exclude-repos, instead of accepting a config where those filters are silently ignored.

Those include/exclude flags only apply to repositories discovered from an org/user scan; explicit --repo URLs skip that filtering path. The CLI returns a clear invalid config error, and GithubConfig comments document that IncludeRepos / ExcludeRepos have no effect when Repos is set explicitly.

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