Split internal/web into subpackages before domain-admin growth.

Lay out view, auth, validate, and handlers under internal/web while keeping
the cmd/panel API unchanged; update roadmap and changelog for web-split closure.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/auth/token.go

@@ -0,0 +1,20 @@
+package auth
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+)
+
+// randomToken returns a URL-safe token with at least nBytes*8 bits of entropy
+// drawn from crypto/rand. Setup and session tokens both use this; the setup
+// token needs >=128 bits (security.md), so callers pass nBytes >= 16.
+//
+// It panics if the system RNG fails: that is unrecoverable and must never be
+// papered over with a weak fallback for a security token.
+func randomToken(nBytes int) string {
+	b := make([]byte, nBytes)
+	if _, err := rand.Read(b); err != nil {
+		panic("crypto/rand failed: " + err.Error())
+	}
+	return base64.RawURLEncoding.EncodeToString(b)
+}