Songs: GOAT TopPresenter Song JSON v2 + rich version-aware editor

[RobyRew]

• TopPresenter Song JSON v2.0.0 (single song per file) — import + export. Superset format: per-song versions, sections with inline chords (ChordPro positions) + bilingual translation lines, arrangement/play-order, section repeat counts, linked media, and rich per-version metadata.
• New importers: TopPresenter Song JSON, ChordPro, plain text. Enriched OpenLyrics (translations, chords) and OpenSong (chords, arrangement). Upgraded PowerPoint importer (filename titles, language guess, chorus-reuse).
• Recursive folder bulk import with duplicate resolution (add as new version / keep both / skip); optional collection name defaults to "Nesortate".
• Scalable song browser: list/grid, indexed search, filters, theme thumbnails.
• Two-pane "song studio" editor: version tabs with inherit/override per-version metadata (incl. per-version songbook), color-coded section cards (drag-reorder, duplicate, repeat x N, inline-chord mode), and a theme-rendered live preview.
• Rendered slide filmstrip with overflow auto-split and theme repeat markers (/: :/, double-bar, pipe, (xN), bis/ter). Presenter sidebar parity and song-specific box sources in the theme editor.
• SwiftData SchemaV2 via automatic additive migration; SongImportVersion is a class to dodge a value-witness miscompile on the large optional struct.
• Tests: GOAT round-trip (incl. per-version overrides), ChordPro, plain text, PowerPoint chorus dedup, recursive import, duplicate->version, auto-split.