Telegram: Webhook-Verwaltung in Einstellungen-Seite

- Backend: DELETE /api/telegram/webhook Endpoint + TelegramService.DeleteWebhook()
- api.js: apiTelegramWebhookInfo(), apiTelegramRegisterWebhook(), apiTelegramDeleteWebhook()
- Settings-Page: Neue 'Telegram Bot' Section (nur für Admins, nur wenn konfiguriert)
  - Status abrufen: Webhook-URL, ausstehende Updates, letzter Fehler, Aktiv-Badge
  - Webhook registrieren: prompt() für Base-URL, POST an Telegram API
  - Webhook entfernen: Bestätigungsdialog + DELETE
- CSS: .telegram-status-box, .tg-status-row, .tg-label, .tg-value, .tg-badge

wwwroot/css/dashboard.css

@@ -375,3 +375,62 @@
   justify-content: center;
   gap: var(--badge-spacing);
 }
+
+/* ── Telegram Settings Status Box ── */
+
+.telegram-status-box {
+  margin: 0 0 var(--box-spacing) 0;
+  border: var(--border-width) solid var(--f1-border);
+  border-radius: var(--border-radius);
+  overflow: hidden;
+}
+
+.tg-status-row {
+  display: flex;
+  align-items: baseline;
+  gap: var(--box-spacing);
+  padding: calc(var(--box-padding) * 0.6) var(--box-padding);
+  border-bottom: var(--border-width) solid var(--f1-border);
+  font-size: var(--font-size);
+}
+
+.tg-status-row:last-child {
+  border-bottom: none;
+}
+
+.tg-status-row.tg-error {
+  background: color-mix(in srgb, var(--danger) 8%, transparent);
+}
+
+.tg-label {
+  flex-shrink: 0;
+  width: 160px;
+  color: var(--text-muted, var(--semi-transparent));
+  opacity: var(--semi-transparent);
+  font-size: calc(var(--font-size) * 0.9);
+}
+
+.tg-value {
+  flex: 1;
+  word-break: break-all;
+  font-family: var(--font-mono, monospace);
+  font-size: calc(var(--font-size) * 0.9);
+}
+
+.tg-badge {
+  display: inline-block;
+  padding: 2px 8px;
+  border-radius: 99px;
+  font-family: var(--font-sans, sans-serif);
+  font-size: calc(var(--font-size) * 0.85);
+}
+
+.tg-badge-ok {
+  background: color-mix(in srgb, var(--success, #22c55e) 15%, transparent);
+  color: var(--success, #22c55e);
+}
+
+.tg-badge-off {
+  background: color-mix(in srgb, var(--warning, #f59e0b) 15%, transparent);
+  color: var(--warning, #f59e0b);
+}