Update card buttons dynamically

User flows when editing a card look like:
- Click "Edit" → the closure buttons are replaced by "Save changes"
- Submit card form → Saves and restores closure buttons
- Press ESC while editing → Cancels and restores closure buttons

Also, renamed for clarity:
- _title.html.erb → _content.html.erb

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

app/controllers/cards_controller.rb

@@ -22,7 +22,6 @@ class CardsController < ApplicationController
 
   def update
     @card.update! card_params
-    redirect_to @card
   end
 
   def destroy