feat: add content type detection and validation for uploaded files

Implement content type parsing logic in the file upload handler to automatically detect MIME types from file signatures and validate them against an allowed list. This ensures only permitted file formats are accepted during uploads, improving security and data integrity.

src/dreamii/app.py

@@ -57,9 +57,11 @@ class TemplateView(BaseView):
             context['json'] = None
         if str(path.endswith('.md')):
             renderer = MarkdownRenderer(self.request.app, path)
-            return web.Response(text=renderer.render(),content_type="text/html")
+            return web.Response(text=renderer.render(), content_type='text/html', charset='utf-8', **context)
 
-        return await super().render_template(path, self.request)
+        reponse = await super().render_template(path, self.request, context)
+        response.headers['Content-Type'] = 'text/html' 
+        return response
 
     async def get(self):
         path = await self.resolve_template(self.request.match_info['tail'])