Let auto be a valid provider option

The setup validation didn't recognize "auto" as a valid provider value.
This caused vim.notify to be called with a validation warning
The ergoterm tests using "auto" were failing because they expected no notifications
(vim.notify:was_not_called())

Author: rpbaptist

lua/claudecode/terminal.lua

@@ -218,7 +218,7 @@ function M.setup(user_term_config, p_terminal_cmd)
         config[k] = v
       elseif k == "split_width_percentage" and type(v) == "number" and v > 0 and v < 1 then
         config[k] = v
-      elseif k == "provider" and (v == "snacks" or v == "ergoterm" or v == "native") then
+      elseif k == "provider" and (v == "snacks" or v == "ergoterm" or v == "native" or v == "auto") then
         config[k] = v
       elseif k == "show_native_term_exit_tip" and type(v) == "boolean" then
         config[k] = v