feat(web): link Impressum version to Gitea source repo

The version line in the Impressum footer ("Calendarr vNN") is now a
subtle link to the Calendarr Gitea repo (git.scarriffle.com), opening
in a new tab. Styled to stay muted at rest and reveal as a link on
hover. Bump APP_VERSION v87 -> v88.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/css/app.css

@@ -63,6 +63,9 @@ input, textarea, [contenteditable="true"], .selectable {
   -webkit-user-select: text; user-select: text;
 }
 a { color: var(--primary); text-decoration: none; }
+/* Version im Impressum verlinkt aufs Gitea-Repo — dezent, erst beim Hover als Link erkennbar */
+.impressum-version-link { color: var(--text-3); text-decoration: none; transition: color .15s ease; }
+.impressum-version-link:hover { color: var(--primary); text-decoration: underline; }
 ::-webkit-scrollbar { width: 6px; height: 6px; }
 ::-webkit-scrollbar-track { background: transparent; }
 ::-webkit-scrollbar-thumb { background: var(--scrollbar); border-radius: 3px; }

frontend/js/calendar.js

@@ -15,7 +15,7 @@ import { APP_VERSION } from './version.js';
 document.title = 'Calendarr';
 document.addEventListener('DOMContentLoaded', () => {
   const imp = document.getElementById('impressum-version');
-  if (imp) imp.textContent = `Calendarr ${APP_VERSION}`;
+  if (imp) imp.innerHTML = `<a class="impressum-version-link" href="https://git.scarriffle.com/Scarriffle/Calendarr" target="_blank" rel="noopener noreferrer" title="Quelltext auf Gitea">Calendarr ${APP_VERSION}</a>`;
   const side = document.getElementById('sidebar-copyright');
   if (side) side.innerHTML = `©&nbsp;2026&nbsp;Scarriffleservices&nbsp;·&nbsp;${APP_VERSION}`;
 });

frontend/js/version.js

@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v87';
+export const APP_VERSION = 'v88';