fixed POST startImport in development

since the user is passed in params, and in POST they're sent as a JSON body, we need to:
1) parse the params from the JSON manually, Sinatra doesn't do that
2) add an OPTIONS route for the CORS preflight

app/server.rb

···
 
     def get_user_did
       if settings.development?
-        if did = params[:user]
+        did = if request.post?
+          json = JSON.parse(request.body.read)
+          request.body.rewind
+          json['user']
+        else
+          params[:user]
+        end
+
+        if did
           return did
         else
           halt json_error('AuthMissing', 'Missing "user" parameter', status: 401)
···
     end
 
     json_response(terms: query.terms, posts: post_uris, cursor: items.last&.cursor)
+  end
+
+  if settings.development?
+    options '/xrpc/blue.feeds.lycan.startImport' do
+      headers['Access-Control-Allow-Origin'] = '*'
+      headers['Access-Control-Allow-Headers'] = 'content-type'
+    end
   end
 
   post '/xrpc/blue.feeds.lycan.startImport' do