Fix MkDocs deployment on public mkdocs-material

[awaismirza92]

Summary

Switch the documentation deployment away from the obsolete private Material Insiders repository and onto the public mkdocs-material package.

Changes

• update the MkDocs deploy workflow to use hatch run default:mkdocs gh-deploy
• remove the GH_C17_DEV_TOKEN dependency from the deploy workflow
• update the Hatch docs dependency to mkdocs-material~=9.7
• remove the obsolete insiders Hatch environment

Validation

• hatch run default:mkdocs build
• GitHub Actions Deploy MkDocs documentation run completed successfully for commit 5a95633.

More: https://squidfunk.github.io/mkdocs-material/blog/2025/11/11/insiders-now-free-for-everyone/

[awaismirza92]

The Linux Conan workflow failed with the error: ConanException: These libraries were built, but were not used in any boost module: {'boost_cobalt_io_ssl'}. The failure should not be caused by the docs-deploy changes in this PR.

Copilot's guess about this error: "The latest main run of the same Linux Conan workflow succeeded on commit ee0dbc6, so this is likely a dependency freshness issue exposed by a later CI run, not a deterministic regression from this docs diff. The --build=missing behavior in the Conan workflow makes that kind of upstream breakage possible."