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/search.rs

@@ -0,0 +1,34 @@
+use async_trait::async_trait;
+use domain::{DomainError, SongSearchPort, SongSummary, SortField, SortOrder};
+
+use crate::repository::SqliteSongRepository;
+use crate::row::{SongRow, row_to_summary, sort_clause};
+
+#[async_trait]
+impl SongSearchPort for SqliteSongRepository {
+    async fn search(
+        &self,
+        query: &str,
+        sort: SortField,
+        order: SortOrder,
+    ) -> Result<Vec<SongSummary>, DomainError> {
+        let escaped = query
+            .replace('\\', "\\\\")
+            .replace('%', "\\%")
+            .replace('_', "\\_");
+        let pattern = format!("%{}%", escaped);
+        let sql = format!(
+            "SELECT id, title, artist, original_key, preview_chords, body FROM songs \
+             WHERE (title LIKE ? ESCAPE '\\' OR artist LIKE ? ESCAPE '\\') {}",
+            sort_clause(sort, order)
+        );
+        let rows = sqlx::query_as::<_, SongRow>(&sql)
+            .bind(&pattern)
+            .bind(&pattern)
+            .fetch_all(&self.pool)
+            .await
+            .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
+        rows.into_iter().map(row_to_summary).collect()
+    }
+}