Adds the /app/decos screen (dual-mode list/editor) mirroring the legacy Blazor
deco form: deco/watermark/graphics/break-content/default-filler/dead-air
sections with mode-gated controls, watermark/graphics multi-selects, break
content with a playlist group->playlist cascade and per-placement uniqueness,
and default-filler/dead-air typeahead pickers. Adds decos/playlists api modules,
artist/multi-collection search wrappers, and regenerated types.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
