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)

Cargo.toml

@@ -1,27 +1,37 @@
 [workspace]
 members = [
-    "crates/api",
-    "crates/common",
+    "crates/adapters/sqlite",
+    "crates/adapters/ug-parser",
+    "crates/api-types",
+    "crates/application",
     "crates/domain",
-    "crates/infrastructure/persistence",
-    "crates/infrastructure/ug-parser",
+    "crates/infra-wiring",
+    "crates/presentation",
 ]
 resolver = "2"
 
 [workspace.dependencies]
-anyhow = "1.0.102"
-reqwest = "0.13.2"
+tokio = { version = "1.51.0", features = ["full"] }
 serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.149"
+anyhow = "1.0.102"
 thiserror = "2.0.18"
-tokio = { version = "1.51.0", features = ["full"] }
 tracing = "0.1.44"
 tracing-subscriber = { version = "0.3.23", features = ["env-filter"] }
+async-trait = "0.1.89"
 uuid = { version = "1.23.0", features = ["v4", "serde"] }
 rand = "0.10.0"
-sqlx = { version = "0.8.6", features = ["runtime-tokio-rustls", "sqlite", "uuid", "macros"] }
-async-trait = "0.1.89"
+reqwest = "0.13.2"
 scraper = "0.23"
+sqlx = { version = "0.8.6", features = ["runtime-tokio-rustls", "sqlite", "uuid", "macros"] }
+axum = { version = "0.8.8", features = ["macros"] }
+
+domain = { path = "crates/domain" }
+application = { path = "crates/application" }
+api-types = { path = "crates/api-types" }
+infra-wiring = { path = "crates/infra-wiring" }
+sqlite = { path = "crates/adapters/sqlite" }
+ug-parser = { path = "crates/adapters/ug-parser" }
 
 [profile.release]
 strip = true