Fix assorted todo-mode bugs (bug#32366)

Fix assorted todo-mode bugs (bug#32366)

* lisp/calendar/todo-mode.el (todo-forward-category): Fix
calculation for skipping backward over archived categories.
(todo-jump-to-category): When hl-line-mode is enabled, force
highlighting to compensate for apparent failure of
post-command-hook to run.
(todo-insert-item--basic): Prevent inserting a new todo item in an
archive category.
(todo-delete-item): Ensure done items separator disappears when
the last done item is deleted.
(todo-edit-item--header): Fix calculation for choosing a month
prior to the current one.
(todo-find-filtered-items-file): Fix use of completing-read,
correcting typo in default value passed to it and confining
history to filtered items files.
(todo-go-to-source-item): Make a noop when point is not on an item.
(todo-save-filtered-items-buffer): Make buffer read-only after
saving and improve buffer name.
(todo-key-bindings-t+a+f): Remove three mistakenly included bindings.
(todo-key-bindings-t+a): Add two mistakenly omitted bindings.