add new functionality and improve backend server structure

- Enhance server functionality and optimize backend code
- Add multi-database support (PostgreSQL, MySQL, SQLite)

server/core_backend-server/migrations/db_driver.go

@@ -0,0 +1,51 @@
+package migrations
+
+import (
+	"strings"
+
+	"github.com/pocketbase/dbx"
+)
+
+// isPostgres checks if the provided database builder is using the PostgreSQL driver.
+func isPostgres(db dbx.Builder) bool {
+	// We check if the table pg_proc exists, which is a system table in PostgreSQL.
+	// This is a reliable way to detect PostgreSQL at runtime without needing
+	// access to the unexported driver name in dbx.
+	var exists bool
+	err := db.NewQuery("SELECT EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'pg_proc')").Row(&exists)
+	if err != nil {
+		// If the query fails, it's likely not PostgreSQL (e.g. SQLite doesn't have information_schema.tables)
+		return false
+	}
+	// Note: in PostgreSQL specifically, pg_proc is in pg_catalog, but information_schema works too
+	// Actually, let's try a simpler one:
+	_, err = db.NewQuery("SELECT version()").Execute()
+	if err != nil {
+		return false
+	}
+	return true
+}
+
+// getDriverName returns the driver name for the provided database builder.
+func getDriverName(db dbx.Builder) string {
+	// PostgreSQL supports 'SELECT version()'
+	var version string
+	err := db.NewQuery("SELECT version()").Row(&version)
+	if err == nil {
+		if strings.Contains(strings.ToLower(version), "postgres") {
+			return "postgres"
+		}
+		// Assume MySQL if version() works but not postgres
+		// (MariaDB also returns version string usually without postgres)
+		return "mysql"
+	}
+
+	// SQLite supports 'SELECT sqlite_version()'
+	var sqliteVersion string
+	err = db.NewQuery("SELECT sqlite_version()").Row(&sqliteVersion)
+	if err == nil {
+		return "sqlite"
+	}
+
+	return "unknown"
+}