fix: reduce subscribe button width to fit content

Adjust the width of the 'S'abonner' button to match the label size
using CSS width: fit-content property.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/pages/compte_abonnement.py

@@ -54,6 +54,7 @@ def _plan_card(meta: dict, trial: int | None, trial_used: bool):
                         if TOUS_ABONNES
                         else "btn btn-primary"
                     ),
+                    style={"width": "fit-content"},
                 ),
             ],
             className="p-4",