/config resumed returned json:None, falling back to prose output even in
--output-format json mode. Adds render_config_json() that produces:
{
"kind": "config",
"cwd": "...",
"loaded_files": N,
"merged_keys": N,
"files": [{"path":"...","source":"user|project|local","loaded":true|false}, ...]
}
Wires it into the SlashCommand::Config resume arm alongside the existing
prose render. Continues the resumed-command JSON parity track (ROADMAP #26).
159 CLI tests pass, fmt clean.
7ec6860d9a