refactor(theme): remove dynamic styling systems and migrate to static CSS architecture

This commit introduces a major internal refactor of the theme, replacing all
dynamic styling mechanisms with a fully static, CSS-based system.

The previous implementation relied on WordPress Customizer settings, PHP-based
style generation, and inline CSS injection for fonts, colors, and header behavior.
These systems have been completely removed and replaced with a deterministic
architecture using CSS variables and dedicated stylesheets.

Key changes:
- Removed dynamic font system (Google/local/inline CSS)
- Removed dynamic color system and Customizer controls
- Removed legacy compatibility layer (legacy-aliases.php)
- Removed custom header support and related UI (header image, text color)
- Eliminated inline <style> injection in wp_head
- Introduced static typography system via fonts.css
- Introduced static color system via colors.css
- Refactored style.css to rely entirely on CSS variables
- Cleaned up conflicting font declarations and redundant rules
- Simplified theme structure and reduced PHP overhead
- Aligned translation template with theme slug (zeitfresser.pot)

Result:
- Improved frontend performance and caching behavior
- Reduced PHP execution and complexity
- Fully deterministic rendering without runtime style mutations
- Cleaner, more maintainable codebase

No visual changes intended.

css/colors.css

@@ -0,0 +1,12 @@
+:root {
+  --site-title-color: #f7f7fa;
+  --primary-color: #f7f7fa;
+  --secondary-color: #f7f7fa;
+  --light-color: #1e1f29;
+  --grey-color: #f7f7fa;
+  --dark-color: #f7f7fa;
+}
+
+body {
+  background-color: #1e1f29;
+}