Extract YAML validation to separate module

- Created yaml-validator.js with pure validation functions
- Removed redundant checkYAMLFormatting function (rely on js-yaml)
- Fixed function shadowing issues by using window._validateYAMLPure
- Updated nginx config to serve JS files with correct MIME type
- Improved error reporting with line/column numbers from js-yaml

Dockerfile

@@ -18,7 +18,7 @@ RUN pip install --no-cache-dir -r backend/requirements.txt
 COPY backend/ /app/backend/
 
 # Copy frontend files
-COPY index.html manage.html /usr/share/nginx/html/
+COPY index.html manage.html yaml-validator.js /usr/share/nginx/html/
 
 # Configure nginx
 RUN echo 'server {\n\
@@ -27,8 +27,10 @@ RUN echo 'server {\n\
     root /usr/share/nginx/html;\n\
     index index.html;\n\
     \n\
-    location / {\n\
-        try_files $uri $uri/ /index.html;\n\
+    # Serve JavaScript files with correct MIME type (must come before location /)\n\
+    location ~* \\.js$ {\n\
+        default_type application/javascript;\n\
+        try_files $uri =404;\n\
     }\n\
     \n\
     location /api {\n\
@@ -36,6 +38,10 @@ RUN echo 'server {\n\
         proxy_set_header Host $host;\n\
         proxy_set_header X-Real-IP $remote_addr;\n\
     }\n\
+    \n\
+    location / {\n\
+        try_files $uri $uri/ /index.html;\n\
+    }\n\
 }' > /etc/nginx/sites-available/default
 
 # Configure supervisor