Add favicon

Same badge as Kestrel's Hall with a B, linked from the index and the
Green Man page.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GrX9qMoNihcWLX3xoJhabw

greenman/index.html

@@ -4,6 +4,7 @@
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Green Man Mask Kit</title>
+<link rel="icon" href="../favicon.svg">
 <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Bricolage+Grotesque:opsz,wght@12..96,600;12..96,700&family=Inter:wght@400;600;700&display=swap">
 <style>
 /* layout: one reading column of guide text; each step is a drawing beside its instructions, stacking on phones */