chore: bump version to 0.5.12

Update package.json version from 0.5.11 to 0.5.12 for the upcoming release.

Changes in this release:
- Batch session deletion (checkbox multi-select, select all, batch delete)
- Visual context length editor (click to edit with custom limits)
- Fix group chat mention keyboard selection (custom dropdown)
- Chat completion sound (auto-play toggle)
- Improved chat message display (filter empty messages)
- Improved update mechanism (dynamic path resolution for Homebrew support)

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "hermes-web-ui",
-  "version": "0.5.11",
+  "version": "0.5.12",
   "description": "Self-hosted AI chat dashboard for Hermes Agent — multi-model (Claude, GPT, Gemini, DeepSeek) web UI with Telegram, Discord, Slack, WhatsApp integration",
   "repository": {
     "type": "git",