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>

package.json

@@ -1,5 +1,5 @@
 {
-  "name": "morning-meeting-planner",
+  "name": "meeting-mixer",
   "version": "1.0.0",
   "private": true,
   "type": "module",