feat: abstracción DB multi-engine — CRUD genérico y openers para SQLite, Postgres, ClickHouse, DuckDB

Funciones Go con interfaz unificada para operaciones DB: open, close, create_table, exec, query, insert_row, insert_batch.
Openers específicos por engine. Tipo DBConfig para configuración común.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions/infra/sqlite_open.go

@@ -0,0 +1,27 @@
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+// SQLiteOpen opens (or creates) a SQLite database file with WAL mode and
+// foreign key support enabled. Returns a ready-to-use *sql.DB or an error.
+// Pass ":memory:" for an in-memory database.
+func SQLiteOpen(path string) (*sql.DB, error) {
+	if path == "" {
+		return nil, fmt.Errorf("sqlite_open: path must not be empty (use ':memory:' for in-memory)")
+	}
+	dsn := fmt.Sprintf("file:%s?_journal_mode=WAL&_foreign_keys=on", path)
+	db, err := sql.Open("sqlite3", dsn)
+	if err != nil {
+		return nil, fmt.Errorf("sqlite_open: open %q: %w", path, err)
+	}
+	if err := db.Ping(); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("sqlite_open: ping %q: %w", path, err)
+	}
+	return db, nil
+}