refactor: Style transaction items for untracked accounts

This commit extends the "Untrack Account" feature by applying a special style to transaction items that belong to an untracked account.

- The transaction item template is modified to apply a "dimmed" style to transactions from untracked accounts.
- The styling follows the precedence: Account (untracked) > Category (muted) > Transaction (hidden).
- The dropdown menu for transaction items now shows "Controlled by account" if the transaction's account is untracked.

app/apps/accounts/views/accounts.py

@@ -155,6 +155,26 @@ def account_delete(request, pk):
     )
 
 
+@only_htmx
+@login_required
+@require_http_methods(["POST"])
+def account_toggle_untracked(request, pk):
+    account = get_object_or_404(Account, id=pk)
+    if account.is_untracked_by(request.user):
+        account.untracked_by.remove(request.user)
+        messages.success(request, _("Account is now tracked."))
+    else:
+        account.untracked_by.add(request.user)
+        messages.success(request, _("Account is now untracked."))
+
+    return HttpResponse(
+        status=204,
+        headers={
+            "HX-Trigger": "updated",
+        },
+    )
+
+
 @only_htmx
 @login_required
 @require_http_methods(["GET"])