docs: migrate content files to TOML frontmatter

Migrate all 17 docs/content/ files from --- YAML to +++ TOML
frontmatter delimiters and key = value syntax.

Update 8 embedded frontmatter examples in 7 documentation pages
to match (configuration, content-organization, getting-started,
security, sections, sitemap, feeds, templates).

Update configuration.md frontmatter reference table: add draft
and aliases fields, correct date type from string to date.

docs/content/features/css.md

@@ -1,8 +1,8 @@
----
-title: CSS Minification
-description: Automatic CSS optimization at build time
-weight: 7
----
++++
+title = "CSS Minification"
+description = "Automatic CSS optimization at build time"
+weight = 7
++++
 
 sukr automatically minifies CSS files in your static directory during the build.