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/fonts.css

@@ -0,0 +1,35 @@
+/* =========================
+   Typography System (Static)
+   ========================= */
+
+:root {
+  --primary-font: 'Oswald', sans-serif;
+  --secondary-font: 'Roboto', sans-serif;
+
+  --site-identity-font-size: 40px;
+  --font-weight: 400;
+  --line-height: 1.6;
+}
+
+/* Base */
+body {
+  font-family: var(--secondary-font);
+  font-weight: var(--font-weight);
+  line-height: var(--line-height);
+}
+
+/* Headlines */
+h1, h2, h3, h4, h5, h6,
+.entry-title {
+  font-family: var(--primary-font);
+  font-weight: var(--font-weight);
+}
+
+/* Site Title */
+.site-title,
+.site-title a {
+  font-family: var(--primary-font);
+  font-size: var(--site-identity-font-size);
+  font-weight: var(--font-weight);
+  line-height: 1.2;
+}