feat: add Forest, Mono, and Cyberpunk color themes

Forest — deep green surfaces (#0a130d base) with green-400 accent.
  Inspired by terminal emulators and dark mode IDE forest schemes.

Mono — near-black zinc-950 surface with pure white/zinc-100 accent.
  Minimal high-contrast monochromatic palette for distraction-free reading.

Cyber — near-black blue surface with neon cyan-400 accent and dracula-palette
  success/danger colors. Cyberpunk aesthetic with neon glow feel.

Changes:
- app.css: three new [data-theme] blocks with full token sets
- +layout.svelte: added forest/mono/cyber to THEMES array (before light themes)
- profile/+page.svelte: same additions with i18n label functions
- messages/*.json: translated names in all 5 locales (en/fr/ru/pt/id)

ui/messages/fr.json

@@ -161,6 +161,9 @@
   "profile_theme_amber": "Ambre",
   "profile_theme_slate": "Ardoise",
   "profile_theme_rose": "Rose",
+  "profile_theme_forest": "Forêt",
+  "profile_theme_mono": "Mono",
+  "profile_theme_cyber": "Cyberpunk",
   "profile_theme_light": "Light",
   "profile_theme_light_slate": "Light Blue",
   "profile_theme_light_rose": "Light Rose",