You shouldn't use the app prop on the <footer> if you want it to be the same width as the content, you should rather put it inside the <v-content>, and then put the absolute prop, just as the following:
<v-app>
<v-navigation-drawer permanent app>
</v-navigation-drawer>
<v-content>
<v-container fluid>
<router-view></router-view>
</v-container>
<v-footer absolute>
<p>©</p>
</v-footer>
</v-content>
</v-app>
Edit/Approach 2: You can also use the inset prop on the <footer> to make an offset from the navigation drawer, if you want to keep the footer out of the <content>.
<v-app>
<v-navigation-drawer permanent app>
</v-navigation-drawer>
<v-content>
<v-container fluid>
<router-view></router-view>
</v-container>
</v-content>
<v-footer inset app>
<p>©</p>
</v-footer>
</v-app>