Rename `autocomplete_replace_underscores` to `autocomplete_keep_underscores`
(default false) so both autocomplete toggles read as "keep" semantics.
`insertTag` now honors the setting for both tag and artist modes, matching
the dropdown display. Embedding insertion always preserves underscores
because the names are filesystem identifiers.
- ui_definitions: rename option, flip default, update label
- scripts/autocomplete: rename handler, checkbox, and config-bridge keys
- javascript/autocomplete: invert render polarity; insertTag takes a `kind`
parameter; drop the artist-mode hardcoded underscore replacement so the
setting controls tags and artists uniformly
Closes#4827
CalamitousFelicitousness
f2227d7785