chore: add changelog for v0.5.12
Add v0.5.12 changelog entry with 6 major improvements:
- 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, better compression)
- Improved update mechanism (dynamic path resolution for Homebrew support)
Full i18n support across all 8 languages (zh, en, de, es, fr, ja, ko, pt).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
ekko
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