feat: add Forest theme (dark green accent on deep forest bg)

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

src/themes.js

@@ -26,6 +26,30 @@ export const THEMES = [
       '--danger':     '#e05555',
     },
   },
+  {
+    id: 'forest',
+    name: 'Forest',
+    accent: '#4caf7d',
+    bg: '#060d08',
+    vars: {
+      '--bg':         '#060d08',
+      '--bg2':        '#0b1410',
+      '--bg3':        '#101a14',
+      '--surface':    '#162218',
+      '--surface2':   '#1d2e20',
+      '--border':     'rgba(255,255,255,0.07)',
+      '--border2':    'rgba(255,255,255,0.12)',
+      '--accent':     '#4caf7d',
+      '--accent2':    '#6dcc99',
+      '--accent-dark':'#2d7a52',
+      '--accent-dim': 'rgba(76,175,125,0.15)',
+      '--accent-glow':'rgba(76,175,125,0.3)',
+      '--text':       '#edfaf2',
+      '--text2':      '#7a9e85',
+      '--text3':      '#455c4a',
+      '--danger':     '#e05555',
+    },
+  },
   {
     id: 'dark-ocean',
     name: 'Dark Ocean',