fix(postgres): prevent Windows path traversal attacks in database names

Add validation for Windows-specific path traversal patterns (`./` and `.\`) 
to prevent directory traversal attacks on Windows systems. This addresses
the security vulnerability where database names could contain current
directory references to access unauthorized paths.

Co-authored-by: Anguel <modelorona@users.noreply.github.com>

Author: claude[bot]

core/src/plugins/postgres/db.go

@@ -49,8 +49,9 @@ func validateDatabase(database string) error {
 		return fmt.Errorf("invalid database name: contains URL-encoded forward slash")
 	}
 
-	// Check for literal path traversal patterns
-	if strings.Contains(database, "../") || strings.Contains(database, "..\\") {
+	// Check for literal path traversal patterns (both Unix and Windows)
+	if strings.Contains(database, "../") || strings.Contains(database, "..\\") ||
+		strings.Contains(database, "./") || strings.Contains(database, ".\\") {
 		return fmt.Errorf("invalid database name: contains path traversal pattern")
 	}