feat: 7 languages — EN, DE, FR, IT, ES, PT, RU

- Full translations for all UI strings in 7 languages
- Language picker shows native names (Français, Italiano, Español, Português, Русский)
- Auto-detection via navigator.languages
- Cyrillic font subset for Russian (Inter, 19KB)
- Footer shared across all languages (untranslated links)

style.css

@@ -7,6 +7,15 @@
   unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
 }
 
+@font-face {
+  font-family: 'Inter';
+  font-style: normal;
+  font-weight: 100 900;
+  font-display: swap;
+  src: url('fonts/inter-cyrillic.woff2') format('woff2');
+  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116;
+}
+
 @font-face {
   font-family: 'JetBrains Mono';
   font-style: normal;