refactor: DDD/CQRS architecture, unified crate layout

- crates: common→application, api→presentation, infrastructure/*→adapters/*
- new crates: api-types, infra-wiring
- domain: errors/, models/, value_objects/, ports/, services/
- application: CQRS use cases (songs/, tabs/) w/ commands, queries, deps
- unified DomainError replaces RepositoryError
- workspace deps, unused dep cleanup
- fix: parse plain-text chord lines (UG drops spans mid-song)
- tests extracted to separate modules (tests/ dirs)

crates/adapters/ug-parser/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "ug-parser"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+domain = { workspace = true }
+tokio = { workspace = true }
+reqwest = { workspace = true }
+scraper = { workspace = true }
+async-trait = { workspace = true }