feat: add copy note content option and migrate AGENTS.md to CLAUDE.md

Add a "Copy note content" option to the note options menu that copies the
event's content field to clipboard. Merge AGENTS.md into CLAUDE.md with
enhanced i18n rules emphasizing append-only locale key ordering.

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

src/i18n/locales/de.ts

@@ -690,6 +690,7 @@ export default {
     'No notes found': 'Keine Notizen gefunden',
     'Try again later or check your connection':
       'Versuchen Sie es später erneut oder überprüfen Sie Ihre Verbindung',
-    'Hide indirect': 'Indirekte ausblenden'
+    'Hide indirect': 'Indirekte ausblenden',
+    'Copy note content': 'Notizinhalt kopieren'
   }
 }