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/utils.js

@@ -1,4 +1,9 @@
-// Shared pure helpers used across modules.
+// Shared pure helpers and constants used across modules.
+
+// Allowed range for the "moderators per day" setting.
+export const MIN_MODERATORS_PER_DAY = 1;
+export const MAX_MODERATORS_PER_DAY = 5;
+
 
 // "YYYY-MM-DD" from numeric parts.
 export function toISO(year, month, day) {