buildUrl() hardcoded 'index' as the homepage, so the menu link for
index.md pointed at /nl. With a different default_page that root URL
served another page, making index.md unreachable.
- Add getEffectiveDefaultPage(): resolves 'auto' to the detected page
and caches the result
- buildUrl() now omits the page segment only for the effective default
page instead of the literal string 'index'
- Route getPage(), generateBreadcrumb(), getContentType() and the
render() template data (default_page, homepage, is_homepage,
home_active_class, current_page, lang switch URLs) through it
- getHomepageTitle() returns t('home') so the home button no longer
duplicates a menu item label
- Drop the now-redundant default_page skip in renderMenu() so every
page stays reachable from the menu
- getAllContentDirs() also skips dot-directories (.git) in the move
dropdown