feat: 16 funciones cybersecurity — análisis, crypto e IO de seguridad

12 funciones puras con implementación real:
HashSHA256, HashMD5, EntropyShannon, IsBase64, IsHex, ExtractURLs,
ParseIPCIDR, IPInRange, NormalizeURL, DetectSQLInjection,
LevenshteinDistance, JaccardSimilarity

4 funciones impuras con implementación real (stdlib):
LookupWhois, ResolveDNS, FetchHTTPHeaders, ScanPortTCP

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

functions/cybersecurity/extract_urls.go

@@ -0,0 +1,14 @@
+package cybersecurity
+
+import "regexp"
+
+var urlRegex = regexp.MustCompile(`https?://[^\s<>"'` + "`" + `\)\]\}]+`)
+
+// ExtractURLs extrae todas las URLs (http/https) encontradas en el texto proporcionado.
+func ExtractURLs(text string) []string {
+	matches := urlRegex.FindAllString(text, -1)
+	if matches == nil {
+		return []string{}
+	}
+	return matches
+}