Fix production build error with proper vendor chunk splitting

- Configure Vite to split vendor chunks (React, DOMPurify, video libs, Supabase)
- Add manual chunk configuration to prevent duplicate module bundling
- Clean Docker build cache and node_modules cache during build
- Update Dockerfile to force clean rebuilds

This should resolve the 'Identifier already declared' error in production
caused by DOMPurify's @xmldom dependency being bundled multiple times.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

vite.config.ts

@@ -18,5 +18,33 @@ export default defineConfig(({ mode }) => ({
   build: {
     // Disable minification completely to avoid variable conflicts
     minify: false,
+    // Prevent duplicate bundling of dependencies
+    rollupOptions: {
+      output: {
+        manualChunks: (id) => {
+          // Vendor chunks for better caching and deduplication
+          if (id.includes('node_modules')) {
+            // Group DOMPurify and its dependencies separately
+            if (id.includes('dompurify') || id.includes('@xmldom')) {
+              return 'vendor-dompurify';
+            }
+            // Group React separately
+            if (id.includes('react') || id.includes('react-dom') || id.includes('react-router')) {
+              return 'vendor-react';
+            }
+            // Group video libraries
+            if (id.includes('video.js') || id.includes('hls.js') || id.includes('plyr')) {
+              return 'vendor-video';
+            }
+            // Group Supabase
+            if (id.includes('@supabase')) {
+              return 'vendor-supabase';
+            }
+            // All other node_modules
+            return 'vendor';
+          }
+        },
+      },
+    },
   },
 }));