feat: add Navidrome client with Subsonic API sync

Add the Navidrome client module that connects to a Navidrome server via
the Subsonic API, fetches artist and album data, and syncs it into the
local SQLite database.

- Add go-subsonic dependency for Subsonic API communication
- Create internal/navidrome/client.go with NavidromeClient wrapper
  - NewClient constructor with token-based auth
  - Ping health check with HTTP status validation
  - GetArtists fetches all artists via getArtists endpoint
  - GetArtistAlbums fetches albums per artist via getArtist endpoint
- Create internal/navidrome/sync.go with sync orchestration
  - SyncArtists upserts artists into artist_settings table
  - SyncAlbums fetches and stores albums for monitored artists
- Add local_albums table (migration 003) with FK to artist_settings
- Add LocalAlbum CRUD operations in internal/database/local_albums.go
- Full test coverage: 19 tests across client and sync packages
- All tests pass, go vet and go fmt clean

internal/database/local_albums.go

@@ -0,0 +1,103 @@
+package database
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// SaveLocalAlbum inserts or replaces a local_albums row.
+func SaveLocalAlbum(db *DB, album *LocalAlbum) error {
+	_, err := db.Conn().Exec(
+		"INSERT OR REPLACE INTO local_albums (id, artist_id, title) VALUES (?, ?, ?)",
+		album.ID, album.ArtistID, album.Title,
+	)
+	if err != nil {
+		return fmt.Errorf("save local album: %w", err)
+	}
+	return nil
+}
+
+// SaveLocalAlbumTx inserts or replaces a local_albums row within an existing transaction.
+func SaveLocalAlbumTx(tx *sql.Tx, album *LocalAlbum) error {
+	_, err := tx.Exec(
+		"INSERT OR REPLACE INTO local_albums (id, artist_id, title) VALUES (?, ?, ?)",
+		album.ID, album.ArtistID, album.Title,
+	)
+	if err != nil {
+		return fmt.Errorf("save local album: %w", err)
+	}
+	return nil
+}
+
+// DeleteLocalAlbumsByArtistTx removes all local_albums rows for a given artist within an existing transaction.
+func DeleteLocalAlbumsByArtistTx(tx *sql.Tx, artistID string) error {
+	_, err := tx.Exec(
+		"DELETE FROM local_albums WHERE artist_id = ?",
+		artistID,
+	)
+	if err != nil {
+		return fmt.Errorf("delete local albums for artist %s: %w", artistID, err)
+	}
+	return nil
+}
+
+// DeleteLocalAlbumsByArtist removes all local_albums rows for a given artist.
+func DeleteLocalAlbumsByArtist(db *DB, artistID string) error {
+	_, err := db.Conn().Exec(
+		"DELETE FROM local_albums WHERE artist_id = ?",
+		artistID,
+	)
+	if err != nil {
+		return fmt.Errorf("delete local albums for artist %s: %w", artistID, err)
+	}
+	return nil
+}
+
+// GetLocalAlbumsByArtist returns all local_albums for a given artist.
+func GetLocalAlbumsByArtist(db *DB, artistID string) ([]LocalAlbum, error) {
+	rows, err := db.Conn().Query(
+		"SELECT id, artist_id, title FROM local_albums WHERE artist_id = ?",
+		artistID,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("query local albums for artist %s: %w", artistID, err)
+	}
+	defer rows.Close()
+
+	var results []LocalAlbum
+	for rows.Next() {
+		var a LocalAlbum
+		if err := rows.Scan(&a.ID, &a.ArtistID, &a.Title); err != nil {
+			return nil, fmt.Errorf("scan local album: %w", err)
+		}
+		results = append(results, a)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("iterate local albums: %w", err)
+	}
+	return results, nil
+}
+
+// GetAllLocalAlbums returns all rows from local_albums.
+func GetAllLocalAlbums(db *DB) ([]LocalAlbum, error) {
+	rows, err := db.Conn().Query(
+		"SELECT id, artist_id, title FROM local_albums",
+	)
+	if err != nil {
+		return nil, fmt.Errorf("query all local albums: %w", err)
+	}
+	defer rows.Close()
+
+	var results []LocalAlbum
+	for rows.Next() {
+		var a LocalAlbum
+		if err := rows.Scan(&a.ID, &a.ArtistID, &a.Title); err != nil {
+			return nil, fmt.Errorf("scan local album: %w", err)
+		}
+		results = append(results, a)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("iterate local albums: %w", err)
+	}
+	return results, nil
+}