Refactor: responsive upload page, fix warnings, CI/CD setup

- Fix MUI v4/React 18 StrictMode warnings (justify→justifyContent, Button migration)
- Responsive UploadDiary: footer visible without scroll, mobile layout centered, overview text hidden on mobile
- Fix Redux selector memoization with createSelector
- RSS sync: auto-refresh PosterSelector after sync, Snackbar feedback with film count
- Add .gitea/workflows/deploy.yml for tag-based CI/CD
- Fix nginx config (default.conf), increase Node heap for Docker build
- Update README

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

nginx-spa.conf

@@ -6,7 +6,7 @@ server {
 
     # Proxy API to backend container
     location /api/ {
-        proxy_pass http://poster-picker-backend-1:5000/api/;
+        proxy_pass http://backend:5000/api/;
         proxy_http_version 1.1;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;