Sprint 13: WebCal-Abo / Kalender-Integration

- GET /api/webcal/token: erzeugt personl. Kalender-Token (einmalig)
- GET /api/webcal/{token}.ics: iCal-Feed mit Health-Erinnerungen,
  eigenen Events, Gassi-Treffen (erstellt + beigetreten), angenommenen Sittings
- RRULE für wiederkehrende Health-Einträge (intervall_tage)
- Migration: users.calendar_token (TEXT UNIQUE)
- Settings: "Kalender abonnieren" öffnet webcal://-Link + Kopier-Button
- api.js: API.webcal.getToken() / resetToken()
- SW-Cache: by-v104, APP_VER: 80

backend/static/js/api.js

@@ -400,6 +400,14 @@ const API = (() => {
     });
   }
 
+  // ----------------------------------------------------------
+  // WEBCAL
+  // ----------------------------------------------------------
+  const webcal = {
+    getToken:    () => get('/webcal/token'),
+    resetToken:  () => del('/webcal/token'),
+  };
+
   // ----------------------------------------------------------
   // ERROR-KLASSE
   // ----------------------------------------------------------
@@ -417,7 +425,7 @@ const API = (() => {
     get, post, put, patch, del, upload,
     auth, dogs, diary, health, tieraerzte, poison,
     places, routes, walks, events, sitting, forum, lost, knigge, weather, push,
-    friends, chat,
+    friends, chat, webcal,
     subscribeToPush, getLocation,
     APIError,
   };

backend/static/js/app.js

@@ -3,7 +3,7 @@
    Router, State-Management, Navigation, Initialisierung.
    ============================================================ */
 
-const APP_VER = '79'; // ← bei jedem Deploy mit Frontend-Änderungen erhöhen
+const APP_VER = '80'; // ← bei jedem Deploy mit Frontend-Änderungen erhöhen
 
 const App = (() => {
 

backend/static/js/pages/settings.js

@@ -78,6 +78,12 @@ window.Page_settings = (() => {
               <span>Push-Benachrichtigungen</span>
               <span style="margin-left:auto;color:var(--c-text-secondary)">›</span>
             </div>
+            <div class="sidebar-item" id="settings-calendar-btn"
+                 style="padding:var(--space-4);border-radius:0;border-bottom:1px solid var(--c-border)">
+              <svg class="ph-icon" aria-hidden="true"><use href="/icons/phosphor.svg#calendar-dots"></use></svg>
+              <span>Kalender abonnieren</span>
+              <span style="margin-left:auto;color:var(--c-text-secondary)">›</span>
+            </div>
             <div class="sidebar-item" id="settings-logout-btn"
                  style="padding:var(--space-4);border-radius:0;cursor:pointer;
                         color:var(--c-danger)">
@@ -171,6 +177,52 @@ window.Page_settings = (() => {
       }
     });
 
+    document.getElementById('settings-calendar-btn')?.addEventListener('click', async () => {
+      try {
+        const { token } = await API.webcal.getToken();
+        const url = `webcal://${location.host}/api/webcal/${token}.ics`;
+        const httpsUrl = `https://${location.host}/api/webcal/${token}.ics`;
+        UI.modal.open({
+          title: `${UI.icon('calendar-dots')} Kalender abonnieren`,
+          body: `
+            <p style="font-size:var(--text-sm);color:var(--c-text-secondary);margin-bottom:var(--space-4)">
+              Abonniere deinen persönlichen Ban-Yaro-Kalender. Er enthält Impf-Erinnerungen,
+              Läufigkeits-Termine, Events und Gassi-Treffen — immer aktuell.
+            </p>
+            <div style="background:var(--c-bg);border-radius:var(--radius-md);
+                        padding:var(--space-3) var(--space-4);
+                        font-size:var(--text-xs);color:var(--c-text-secondary);
+                        word-break:break-all;margin-bottom:var(--space-4)">
+              ${UI.escHtml(httpsUrl)}
+            </div>
+            <div style="display:flex;flex-direction:column;gap:var(--space-2)">
+              <a href="${UI.escHtml(url)}"
+                 class="btn btn-primary"
+                 style="text-align:center">
+                ${UI.icon('calendar-dots')} In Kalender-App öffnen
+              </a>
+              <button class="btn btn-secondary" id="cal-copy-btn">
+                ${UI.icon('clipboard-text')} URL kopieren
+              </button>
+            </div>
+            <p style="font-size:var(--text-xs);color:var(--c-text-muted);margin-top:var(--space-4)">
+              Tipp: iOS → Einstellungen › Kalender › Accounts › Account hinzufügen › Andere › Kalenderabo
+            </p>
+          `,
+        });
+        document.getElementById('cal-copy-btn')?.addEventListener('click', async () => {
+          try {
+            await navigator.clipboard.writeText(httpsUrl);
+            UI.toast.success('URL kopiert.');
+          } catch {
+            UI.toast.warning('Kopieren nicht möglich — URL oben manuell kopieren.');
+          }
+        });
+      } catch {
+        UI.toast.error('Kalender-Token konnte nicht geladen werden.');
+      }
+    });
+
     document.getElementById('toggle-pocket-mode')?.addEventListener('change', e => {
       localStorage.setItem('by_pocket_mode', String(e.target.checked));
       UI.toast.info(e.target.checked