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/calendar.js

@@ -2,7 +2,8 @@ import { state, saveState } from './app.js';
 import { getWorkdays, generatePlan } from './algorithm.js';
 import { toggleHoliday, toggleClosure, addHistoryEntries, removeHistoryEntry } from './data.js';
 import { exportSchedule, downloadBlob } from './excel.js';
-import { toISO, monthPrefix, getWeekday, buildNameMap } from './utils.js';
+import { toISO, monthPrefix, getWeekday, buildNameMap,
+  MIN_MODERATORS_PER_DAY, MAX_MODERATORS_PER_DAY } from './utils.js';
 
 const MONTHS = ['Januar','Februar','März','April','Mai','Juni',
   'Juli','August','September','Oktober','November','Dezember'];
@@ -61,7 +62,7 @@ export function renderCalendar() {
 
   const slotsSel = document.createElement('select');
   slotsSel.id = 'cal-slots';
-  for (let n = 1; n <= 5; n++) {
+  for (let n = MIN_MODERATORS_PER_DAY; n <= MAX_MODERATORS_PER_DAY; n++) {
     const opt = document.createElement('option');
     opt.value = String(n);
     opt.textContent = String(n);