feat: dark theme polish — fix sidebar layout, update button, chat input & theme switching

- Fix sidebar footer layout: separate update button from version row
- Replace custom update-hint with NButton for proper dark mode support
- Darken chat input background in dark theme for better contrast
- Fix system theme listener always applying dark mode

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "hermes-web-ui",
-  "version": "0.2.9",
+  "version": "0.3.0",
   "description": "Web dashboard for Hermes Agent — multi-platform AI chat, session management, scheduled jobs, usage analytics & channel configuration (Telegram, Discord, Slack, WhatsApp)",
   "repository": {
     "type": "git",
@@ -92,4 +92,4 @@
     "vitest": "^3.2.4",
     "vue-tsc": "^3.2.6"
   }
-}
+}