Replacing the paid button with the cancel/hide action block cut the old
markup at the first <% end %>, which belonged to the button's inner
if/else, leaving a stray </button></form><% end %> behind. show.erb no
longer compiled and every admin invoice page returned 500; nothing
rendered that page in tests.
Remove the leftovers, render the page in every state (pending, paid,
cancelled, hidden), and compile every view in a test so an unbalanced
template fails CI even when no test visits that page.
Assisted-by: Claude:opus-5
An invoice issued by mistake could only be left pending or marked paid.
Add cancel (with an optional reason) and reinstate. Cancelling renders a
third PDF variant with a diagonal CANCELLED stamp and the date/reason,
and it becomes the current one, so the client's link and download show
the invoice as void. Cancelled wins over paid in the status, and marking
a cancelled invoice paid is refused.
Superusers can also hide an invoice: it disappears from the admin list,
dashboard and invoice pages for every other user, while the client's
public link keeps working.
Assisted-by: Claude:opus-5
