* main: (24 commits)
  docs: Use definition lists for parameter descriptions to enable full markdown support (#901)
  docs(layout_columns): Add example app (#903)
  fix(layout_columns): Remove use of enum for breakpoints (#912)
  Express: don't automatically put strings in a `<pre>` block (#905)
  Deprecate `nav()` in favor of `nav_panel()` (#876)
  chore: Remove unused import
  refactor(layout_column_wrap): Use helper for wrapping children (#910)
  fix(layout_columns): Don't apply fillable class to layout container (#909)
  Add output to React template (#908)
  fix(layout_columns): Add missing `bslib-mb-spacing` class (#906)
  Custom component template updates (#874)
  fix(layout_columns): If the breakpoint name is an enum, need to collect the value (#902)
  chore: exclude `_dev/` folder (#897)
  feat: Add `ui.layout_columns()` (#856)
  Update VS Code settings file
  Express: change default page function to page_fixed (#892)
  Better messages for `AttributeError` in Shiny Express (#888)
  Fix 0.6.0 release date
  Fix failing express tests (#887)
  Explain why function is called twice
  ...

Fixes #880

Fixes #917