Add mock fetcher and service tests for imgcache

Introduces Fetcher interface, mock implementation for testing,
and ApplyMigrations helper for test database setup.

internal/database/database.go

@@ -166,3 +166,77 @@ func (s *Database) runMigrations(ctx context.Context) error {
 func (s *Database) DB() *sql.DB {
 	return s.db
 }
+
+// ApplyMigrations applies all migrations to the given database.
+// This is useful for testing where you want to use the real schema
+// without the full fx lifecycle.
+func ApplyMigrations(db *sql.DB) error {
+	ctx := context.Background()
+
+	// Create migrations tracking table
+	_, err := db.ExecContext(ctx, `
+		CREATE TABLE IF NOT EXISTS schema_migrations (
+			version TEXT PRIMARY KEY,
+			applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
+		)
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to create migrations table: %w", err)
+	}
+
+	// Get list of migration files
+	entries, err := schemaFS.ReadDir("schema")
+	if err != nil {
+		return fmt.Errorf("failed to read schema directory: %w", err)
+	}
+
+	// Sort migration files by name (001.sql, 002.sql, etc.)
+	var migrations []string
+	for _, entry := range entries {
+		if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".sql") {
+			migrations = append(migrations, entry.Name())
+		}
+	}
+	sort.Strings(migrations)
+
+	// Apply each migration that hasn't been applied yet
+	for _, migration := range migrations {
+		version := strings.TrimSuffix(migration, filepath.Ext(migration))
+
+		// Check if already applied
+		var count int
+		err := db.QueryRowContext(ctx,
+			"SELECT COUNT(*) FROM schema_migrations WHERE version = ?",
+			version,
+		).Scan(&count)
+		if err != nil {
+			return fmt.Errorf("failed to check migration status: %w", err)
+		}
+
+		if count > 0 {
+			continue
+		}
+
+		// Read and apply migration
+		content, err := schemaFS.ReadFile(filepath.Join("schema", migration))
+		if err != nil {
+			return fmt.Errorf("failed to read migration %s: %w", migration, err)
+		}
+
+		_, err = db.ExecContext(ctx, string(content))
+		if err != nil {
+			return fmt.Errorf("failed to apply migration %s: %w", migration, err)
+		}
+
+		// Record migration as applied
+		_, err = db.ExecContext(ctx,
+			"INSERT INTO schema_migrations (version) VALUES (?)",
+			version,
+		)
+		if err != nil {
+			return fmt.Errorf("failed to record migration %s: %w", migration, err)
+		}
+	}
+
+	return nil
+}