feat: add auto_save_on_select_new_entry config option

Problem: users who want hands-off behaviour had no way to skip the
`prompt_save_on_select_new_entry` confirmation dialog — enabling the
prompt meant always being asked, with no silent auto-save path.

Solution: add `auto_save_on_select_new_entry` (default `false`) which,
when true, calls `M.save()` and proceeds immediately instead of showing
the confirm dialog. Includes type annotations, vimdoc, and upstream
tracker update for stevearc/oil.nvim#393.

lua/canola/init.lua

@@ -788,6 +788,10 @@ M.select = function(opts, callback)
     end
   end
   if any_moved and config.prompt_save_on_select_new_entry then
+    if config.auto_save_on_select_new_entry then
+      M.save()
+      return finish()
+    end
     local ok, choice = pcall(vim.fn.confirm, 'Save changes?', 'Yes\nNo', 1)
     if not ok then
       return finish()