Fix prefix URL routing for encoded CIDR notation

Change route from wildcard /prefix/* to explicit /prefix/{prefix}/{len}
to properly handle URL-encoded IPv6 addresses with CIDR notation.

- Separate prefix and length into individual path parameters
- Add prefixURL template function for generating correct links
- Remove url.QueryUnescape from handlers (chi handles decoding)

internal/templates/templates.go

@@ -5,6 +5,7 @@ import (
 	_ "embed"
 	"html/template"
 	"net/url"
+	"strings"
 	"sync"
 	"time"
 
@@ -43,8 +44,9 @@ var (
 )
 
 const (
-	hoursPerDay  = 24
-	daysPerMonth = 30
+	hoursPerDay        = 24
+	daysPerMonth       = 30
+	cidrPartCount      = 2 // A CIDR has two parts: prefix and length
 )
 
 // timeSince returns a human-readable duration since the given time
@@ -80,6 +82,20 @@ func timeSince(t time.Time) string {
 	return t.Format("2006-01-02")
 }
 
+// prefixURL generates a URL path for a prefix in CIDR notation.
+// Takes a prefix like "192.168.1.0/24" and returns "/prefix/192.168.1.0/24"
+// with the prefix part URL-encoded to handle IPv6 colons.
+func prefixURL(cidr string) string {
+	// Split CIDR into prefix and length
+	parts := strings.SplitN(cidr, "/", cidrPartCount)
+	if len(parts) != cidrPartCount {
+		// Fallback if no slash found
+		return "/prefix/" + url.PathEscape(cidr) + "/0"
+	}
+
+	return "/prefix/" + url.PathEscape(parts[0]) + "/" + parts[1]
+}
+
 // initTemplates parses all embedded templates
 func initTemplates() {
 	var err error
@@ -90,6 +106,7 @@ func initTemplates() {
 	funcs := template.FuncMap{
 		"timeSince":        timeSince,
 		"urlEncode":        url.QueryEscape,
+		"prefixURL":        prefixURL,
 		"appName":          func() string { return version.Name },
 		"appAuthor":        func() string { return version.Author },
 		"appAuthorURL":     func() string { return version.AuthorURL },