Add ChordPro lyrics support

[RedyAu]

Summary

• add a new dart_chordpro parser package in the Reformatus org and consume it as a pinned git dependency
• extend the app lyrics parsing layer with format-agnostic verse, line, comment, and chord segment primitives
• add ChordPro support for inline chords, verse/chorus/bridge blocks, chorus recall, comments, and page breaks while keeping OpenSong rendering on the same UI path

Companion repo

• https://github.com/reformatus/dart_chordpro

Validation

• dart analyze in dart_chordpro
• dart test in dart_chordpro
• flutter analyze lib/data/song/lyrics/format.dart lib/data/song/lyrics/parser.dart lib/services/song/verse_tag_pretty.dart lib/ui/song/lyrics/view.dart test/data/lyrics_parser_test.dart test/data/song_from_bank_api_json_test.dart
• flutter test test/data

Notes

• full-project flutter analyze still reports existing warnings in lib/services/app_links/cue_compression.dart, lib/services/cue/compression.dart, and test/router/imperative_url_reflection_test.dart; this PR does not add new analyzer issues