The current [user
guide](https://tox.wiki/en/latest/user_guide.html#basic-example) link
returns a 404 error. I've updated the link to the getting started page.

ty 0.0.17 introduced new diagnostics that cause CI failures. The
`redundant-final-classvar` warning flags `Final[ClassVar[...]]` in
`docs/tox_conf.py` since `Final` already implies class-level scope,
making `ClassVar` redundant. The `call-top-callable` errors in
`src/tox/config/of_type.py` arise because `callable()` cannot statically
narrow `Callable[[], T] | T` when `T` is an unconstrained type variable
— the value could itself be callable, so ty can't determine the call
signature.

Removed the redundant `Final` wrapper and added `ty:
ignore[call-top-callable]` suppressions for the two `callable()` guards,
which are a valid runtime pattern that ty cannot verify statically.

The Diataxis restructure moved documentation pages into subdirectories
(e.g. `config.html` to `reference/config.html`, `cli_interface.html` to
`reference/cli.html`) and removed several pages entirely
(`upgrading.html`, `faq.html`, all `example/*.html` pages from tox 3).
External links from Stack Overflow and other sites now return 404.

This adds `sphinx-reredirects` to generate HTML redirect pages at build
time, keeping the configuration version-controlled alongside the docs.
Pages that moved get redirected to their new location, and removed pages
redirect to the landing page. URL fragments are preserved so links like
`config.html#conf-description` still resolve correctly.

Fixes #3806

…ch (#3810)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Bernát Gábor <bgabor8@bloomberg.net>

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Bernát Gábor <bgabor8@bloomberg.net>

…tion (#3816)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>