settings_fill_json(v) writes every saved setting into an object the caller keeps, making a Value
only for a key seen the first time (value_set_str / value_set_int): Maroon Lake's Settings pages
rebuilt the whole tree on every change and dropped the old one. A text read from a file is interned,
and so is a muted card's key ludic.hints does not know, so the parsed tree can be let go whole.
Test: the store filled into a kept object changes its Values in place (6 tests pass).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>