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>

packages/client/src/data/changelog.ts

@@ -5,6 +5,18 @@ export interface ChangelogEntry {
 }
 
 export const changelog: ChangelogEntry[] = [
+  {
+    version: '0.5.12',
+    date: '2026-05-06',
+    changes: [
+      'changelog.new_0_5_12_1',
+      'changelog.new_0_5_12_2',
+      'changelog.new_0_5_12_3',
+      'changelog.new_0_5_12_4',
+      'changelog.new_0_5_12_5',
+      'changelog.new_0_5_12_6',
+    ],
+  },
   {
     version: '0.5.11',
     date: '2026-05-05',