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>

js/algorithm.js

@@ -1,5 +1,8 @@
 import { toISO, getWeekday } from './utils.js';
 
+// Score penalty applied when a candidate is low-priority on the given weekday.
+const LOW_PRIORITY_PENALTY = 5;
+
 function isOnVacation(employee, isoDate) {
   return employee.constraints.vacations.some(v => v.from <= isoDate && isoDate <= v.to);
 }
@@ -60,7 +63,7 @@ function scoreCandidate(employee, isoDate, histCount, randomFn) {
   let score = -myTotal;
 
   // Low priority: increase negative score (less likely to be picked)
-  if (employee.constraints.lowPriorityDays.includes(wd)) score -= 5;
+  if (employee.constraints.lowPriorityDays.includes(wd)) score -= LOW_PRIORITY_PENALTY;
 
   // Jitter ±0.49
   score += (randomFn() - 0.5) * 0.98;