Initial commit: shared Go utilities (ssr, stringsx)

Extracted from sweeper to share across Go projects:
- ssr: template caching and SSR writer
- stringsx: string helpers

stringsx/stringsx.go

@@ -0,0 +1,9 @@
+// Package stringsx provides string-related helpers.
+package stringsx
+
+import "strings"
+
+// IsBlank reports whether a string contains only whitespace.
+func IsBlank(s string) bool {
+	return strings.TrimSpace(s) == ""
+}