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/src/FileSpan.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace SourceSpan;
+
+interface FileSpan extends SourceSpanWithContext
+{
+    public function getFile(): SourceFile;
+
+    public function getStart(): FileLocation;
+
+    public function getEnd(): FileLocation;
+
+    public function expand(FileSpan $other): FileSpan;
+
+    /**
+     * Return a span from $start bytes (inclusive) to $end bytes
+     * (exclusive) after the beginning of this span
+     */
+    public function subspan(int $start, ?int $end = null): FileSpan;
+}