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/sqlite/src/row.rs

@@ -0,0 +1,42 @@
+use domain::{DomainError, SongMeta, SongSummary, SortField, SortOrder};
+use uuid::Uuid;
+
+#[derive(sqlx::FromRow)]
+pub(crate) struct SongRow {
+    pub(crate) id: String,
+    pub(crate) title: String,
+    pub(crate) artist: String,
+    pub(crate) original_key: Option<String>,
+    pub(crate) preview_chords: String,
+    pub(crate) body: String,
+}
+
+pub(crate) fn sort_clause(field: SortField, order: SortOrder) -> &'static str {
+    match (field, order) {
+        (SortField::Title, SortOrder::Asc) => "ORDER BY title ASC",
+        (SortField::Title, SortOrder::Desc) => "ORDER BY title DESC",
+        (SortField::Artist, SortOrder::Asc) => "ORDER BY artist ASC",
+        (SortField::Artist, SortOrder::Desc) => "ORDER BY artist DESC",
+        (SortField::Date, SortOrder::Asc) => "ORDER BY created_at ASC",
+        (SortField::Date, SortOrder::Desc) => "ORDER BY created_at DESC",
+    }
+}
+
+pub(crate) fn row_to_summary(row: SongRow) -> Result<SongSummary, DomainError> {
+    let id =
+        Uuid::parse_str(&row.id).map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+    let preview_chords: Vec<String> = serde_json::from_str(&row.preview_chords)
+        .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+    Ok(SongSummary {
+        id,
+        meta: SongMeta {
+            title: row.title,
+            artist: row.artist,
+            original_key: row.original_key,
+            capo: None,
+            tuning: None,
+            tempo: None,
+        },
+        preview_chords,
+    })
+}