Web: remove version from tab title, fix month event packing, add day overflow popup

- Tab title shows only "Calendarr" (version stays in sidebar/impressum)
- Fix lane assignment in month view: use 2D per-column occupancy grid instead of
  global colEnd tracking; eliminates empty rows caused by non-overlapping events
  being pushed to lower lanes
- "+N weitere" now opens an inline popup listing all events for that day
  (all-day first, then by time); clicking an event opens its detail popup
- Double-click on day cell navigates to day view (was already implemented)
- Remove hardcoded "v18" from login screen impressum button
- Bump version to v49

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/js/calendar.js

@@ -9,8 +9,8 @@ import { openDatePicker, formatDtDisplay } from './date-picker.js';
 import { t, setLang, getLang } from './i18n.js';
 import { APP_VERSION } from './version.js';
 
-// Version sofort beim Modul-Load ueberall sichtbar setzen.
-document.title = `Calendarr ${APP_VERSION}`;
+// Version im Impressum/Sidebar sichtbar, nicht im Tab-Titel.
+document.title = 'Calendarr';
 document.addEventListener('DOMContentLoaded', () => {
   const imp = document.getElementById('impressum-version');
   if (imp) imp.textContent = `Calendarr ${APP_VERSION}`;
@@ -543,7 +543,7 @@ function updateTitle() {
   titleEl.innerHTML =
     `<span class="view-title-main">${main}</span>` +
     (year ? `<span class="view-title-year">${year}</span>` : '');
-  document.title = `Calendarr ${APP_VERSION} - ${fullText}`;
+  document.title = `Calendarr – ${fullText}`;
 }
 
 function updateViewButtons() {