Removing bootstrap5 Templates

The bootstrap5 templates are very out of date because all of the development has gone into daisyUI templates. The continuing presence of the bootstrap5 templates creates confusion. I have in mind a future simplification and modularisation of the template system (something along the lines of template packs like crispy-forms does) but that won't be for a while. So in the meantime, it's better to just remove bootstrap5 completely. This is the plan to do that.

Task List

1. Remove the entire app template pack at src/powercrud/templates/powercrud/bootstrap5/ plus every file underneath it.
2. Drop the sample project equivalents inside src/sample/templates/sample/bootstrap5/.
3. Delete all bootstrap5-specific crispy helper code in src/powercrud/mixins/htmx_mixin.py.
4. Remove the template pack handling in src/powercrud/management/commands/pcrud_mktemplate.py.
5. Update src/sample/filters.py so crispy helpers no longer reference bootstrap5/layout/inline_field.html.
6. Strip bootstrap5 from src/tests/settings.py (allowed packs, installed apps) and from src/config/settings.py.
7. Remove the dependency on crispy-bootstrap5 from pyproject.toml, uv.lock, and any other dependency manifests.
8. Documentation cleanup:
   1. Update README.md so it no longer mentions bootstrap5.
   2. Update docs/mkdocs/index.md to remove any bootstrap5 references.
   3. Update docs/mkdocs/guides/styling_tailwind.md to reflect the removal.
   4. Update docs/mkdocs/reference/mgmt_commands.md so it no longer references bootstrap5.
   5. Update docs/mkdocs/guides/getting_started.md to remove bootstrap5 references.
   6. Update docs/mkdocs/reference/config_options.md to mention only current frameworks.
9. Scan the repository for bootstrap5 references after the above work to ensure no lingering docs or comments remain.