chore: unify name to "Meeting Mixer", README tech stack, name magic numbers (#16)

- Canonical name "Meeting Mixer" everywhere: <title>, README, .vch-description
  (now non-technical per convention) and package.json (meeting-mixer).
- README gains a Tech-Stack section and an accurate, non-misleading port note.
- Magic numbers replaced by named constants: LOW_PRIORITY_PENALTY in
  algorithm.js; MIN/MAX_MODERATORS_PER_DAY in utils.js, used by data.js,
  calendar.js and app.js.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

index.html

@@ -4,7 +4,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'self' https://cdn.sheetjs.com; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src https://fonts.gstatic.com; img-src 'self' data:; object-src 'none'; base-uri 'self'">
-  <title>Morning Meeting Planner</title>
+  <title>Meeting Mixer</title>
   <link rel="preconnect" href="https://fonts.googleapis.com">
   <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
   <link href="https://fonts.googleapis.com/css2?family=Bebas+Neue&family=Space+Grotesk:wght@400;500;600;700&display=swap" rel="stylesheet">