feat: site-wide Swing Music player, persistent storage, mobile UX polish

- SiteWideMusicDock component at app level; persists across all routes
- Dock + player merged into single expandable panel
- Remove non-functional Hide button; one Minimize/Open control
- Swing Music label and action button on same row
- Mobile: dock z-index above player, larger touch target on iPad
- entrypoint.sh: seeds admin-content.json only on first boot/fresh volume
- Dockerfile: seed in /app/data-seed; live data in /app/data (volume)
- shell-with-music-bar padding on project and admin pages

Dockerfile

@@ -18,9 +18,15 @@ RUN npm ci --omit=dev
 
 COPY --from=build /app/dist ./dist
 COPY server.js ./server.js
-COPY data ./data
+
+# Copy seed data to a separate directory so the entrypoint can seed /app/data
+# only when no live data exists yet — upgrades never overwrite existing data.
+COPY data ./data-seed
 
 RUN mkdir -p /app/data
 
+COPY entrypoint.sh ./entrypoint.sh
+RUN chmod +x ./entrypoint.sh
+
 EXPOSE 4173
-CMD ["node", "server.js"]
+ENTRYPOINT ["./entrypoint.sh"]