feat(ui): language persistence, theme fix, font/size settings, header quick-access

- Fix language not persisting after refresh: save locale in user_settings,
  set PARAGLIDE_LOCALE cookie from DB preference on server load
- Fix theme change not applying: context setter was mismatched (setTheme vs current)
- Add font family (system/serif/mono) and text size (sm/md/lg/xl) user settings
  stored in DB and applied via CSS custom properties
- Add theme color dots and language picker to desktop header for quick access
- Footer locale switcher now saves preference to DB before switching
- Remove change password section (OAuth-only, no password login)
- Fix active sessions piling up: reuse existing session on re-login via OAuth
- Extend speed step cycle to include 2.5× and 3.0× (matching profile slider)
- Replace plain checkbox with modern toggle switch for auto-next setting
- Fix catalogue status labels (ongoing/completed) to use translation keys
- Add font family and text size translation keys to all 5 locale files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/messages/ru.json

@@ -391,5 +391,15 @@
   "reader_generate_samples": "Сгенерировать недостающие образцы",
   "reader_voice_applies_next": "Новый голос применится при следующем нажатии «Воспроизвести».",
   "reader_choose_voice": "Выбрать голос",
-  "reader_generating_narration": "Генерация озвучки…"
+  "reader_generating_narration": "Генерация озвучки…",
+
+  "profile_font_family": "Шрифт",
+  "profile_font_system": "Системный",
+  "profile_font_serif": "Serif",
+  "profile_font_mono": "Моноширинный",
+  "profile_text_size": "Размер текста",
+  "profile_text_size_sm": "Маленький",
+  "profile_text_size_md": "Нормальный",
+  "profile_text_size_lg": "Большой",
+  "profile_text_size_xl": "Очень большой"
 }