feat(template): drop docs-site, fold audience/visibility into one open_source question

[ichoosetoaccept]

Remove the generated documentation site entirely: zensical, mkdocstrings,
the docs/ tree, the Pages workflow and GitLab pages job, the docs-build hook
and all related dependencies. A scaffolded project now keeps a README and
CHANGELOG; published docs are the user's own responsibility once a project
actually has an audience.

Collapse the public/private axis — previously asked three times via
project_audience, project_visibility and use_community_health_files — into a
single open_source question that gates the LICENSE and community-health files.
It defaults to true on GitHub, false elsewhere.

Remaining opinions stay opinionated with static defaults: CI on, heavy hooks off.

Closes #

Note

Drop docs-site scaffolding and replace audience/visibility questions with a single open_source flag in the project template

• Removes the project_audience, project_visibility, use_community_health_files, and use_docs questions from copier.yml, replacing them with a single open_source boolean (defaults to true when repository_provider == 'github.com').
• Deletes all docs-site template files (MkDocs pages, CSS overrides, zensical config) and removes docs-related steps from GitHub Actions and GitLab CI workflows.
• Gates LICENSE, community-health files (CODE_OF_CONDUCT, CONTRIBUTING, SECURITY, issue/PR templates), license metadata in pyproject.toml, and PyPI publishing defaults on open_source.
• Sets use_ci default to true and use_heavy_hooks default to false; heavy hooks now only cover coverage, not docs builds.
• Behavioral Change: any previously generated project relying on project_visibility, use_docs, or use_community_health_files answers will need to migrate to the new open_source flag.

^{Macroscope summarized d8507d3.}

[ichoosetoaccept]

This change is part of the following stack:

• feat(template): drop docs-site, fold audience/visibility into one open_source question #327 ◀

_{Change managed by git-spice.}

[macroscopeapp]

Approvability

Verdict: Needs human review

This PR removes the docs-site feature entirely and consolidates multiple configuration questions into a single open_source toggle. These are significant template capability changes that alter what generated projects will contain, warranting human review of the product direction.

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