Bundle system-prompt.txt and copy to persistent volume on startup

- Include SchrottBot personality as bundled default
- Copy to data/ on first startup (persistent, editable)
- Load from persistent location after first run
- Changes survive container rebuilds

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

Dockerfile

@@ -6,6 +6,7 @@ COPY package*.json ./
 RUN npm ci --only=production
 
 COPY dist ./dist
+COPY src/system-prompt.txt ./dist/system-prompt.txt
 
 # Persistent data directory
 VOLUME ["/app/data"]