Fix pixel persistence and improve mobile UX

- Fix pixel data storage to include user information (userId, username, timestamp)
- Enhance zoom controls to center properly without drift
- Improve mobile modal centering with flexbox layout
- Add dynamic backend URL detection for network access
- Fix CORS configuration for development mode
- Add mobile-optimized touch targets and safe area support

.claude/settings.local.json

@@ -14,7 +14,9 @@
       "Bash(mv:*)",
       "Bash(move start-dev.js scripts )",
       "Bash(move setup.js scripts)",
-      "Bash(npm run type-check:*)"
+      "Bash(npm run type-check:*)",
+      "Bash(git push:*)",
+      "Bash(git add:*)"
     ],
     "deny": [],
     "ask": [],