CMS 2.0 - Theme engine, logging, admin improvements

Major changes:
- New ThemeManager with Twig templating and SCSS compilation
- Dynamic themes system (themes/default, themes/demo)
- LogManager with SQLite storage and syslog forwarding
- RequestLogger with static helper methods
- Admin UI overhaul (Bootstrap 5, dark mode)
- Admin config page with logging and theme settings
- Admin logs page with filters and search
- Removed legacy Mustache templates
- Removed test plugin and theme
- Composer dependencies: Twig, scssphp, CommonMark, MaxMind GeoIP

vendor/scssphp/source-span/README.md

@@ -0,0 +1,22 @@
+# SourceSpan
+
+`scssphp/source-span` is a library for tracking locations in source code. It's designed
+to provide a standard representation for source code locations and spans so that
+disparate packages can easily pass them among one another, and to make it easy
+to generate human-friendly messages associated with a given piece of code.
+
+The most commonly-used interface is the package's namesake, `SourceSpan\SourceSpan`. It
+represents a span of characters in some source file, and is often attached to an
+object that has been parsed to indicate where it was parsed from. It provides
+access to the text of the span via `SourceSpan::getText()` and can be used to produce
+human-friendly messages using `SourceSpan::message()`. It's most simple implementation
+is `SourceSpan\SimpleSourceSpan` which holds directly the span information.
+
+When parsing code from a file, `SourceSpan\SourceFile` is useful. Not only does it provide
+an efficient means of computing line and column numbers, `SourceFile#span()`
+returns special `FileSpan`s that are able to provide more context for their
+error messages.
+
+## Credits
+
+This library is a PHP port of the [Dart `source_span` package](https://github.com/dart-lang/source_span).