Fix: Simplify integration and fix admin template

- Removed settings/navigation from appinfo/info.xml
  - These sections can cause routing conflicts
  - App now relies purely on routes.php
- Simplified Application.php
  - Removed manual service/controller registration
  - Let Nextcloud DI framework handle it automatically
- Fixed admin template to use Nextcloud standards
  - Removed non-standard style() call
  - Added proper l10n support with p($l->t(...))
  - Clean template structure
- Created css/admin.css
  - Nextcloud-compatible styling
  - Matches design language
- Created js/admin.js
  - Handles Save Configuration button
  - Handles Test Connection button
  - Uses OC, OC.Notification APIs

This should fix admin page not appearing issue.
Users can access via: Settings → Administration → Additional Settings

analyticshub/css/admin.css

@@ -0,0 +1,60 @@
+#analytics-hub-settings {
+    max-width: 800px;
+    margin: 0 auto;
+    padding: 20px;
+}
+
+.analytics-hub-settings__section {
+    margin-bottom: 30px;
+}
+
+.analytics-hub-settings__field {
+    margin-bottom: 20px;
+}
+
+.analytics-hub-settings__field label {
+    display: block;
+    font-weight: 600;
+    margin-bottom: 8px;
+}
+
+.analytics-hub-settings__field input {
+    width: 100%;
+    padding: 10px;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+    font-size: 14px;
+    box-sizing: border-box;
+}
+
+.analytics-hub-settings__hint {
+    font-size: 13px;
+    color: #666;
+    margin-top: 8px;
+    line-height: 1.4;
+}
+
+.analytics-hub-settings__actions {
+    display: flex;
+    gap: 10px;
+    margin-top: 20px;
+}
+
+.analytics-hub-settings__actions button {
+    padding: 12px 24px;
+    border: none;
+    border-radius: 6px;
+    font-size: 14px;
+    font-weight: 600;
+    cursor: pointer;
+}
+
+.analytics-hub-settings__actions .primary {
+    background-color: #0078d4;
+    color: white;
+}
+
+.analytics-hub-settings__actions .secondary {
+    background-color: #6c757d;
+    color: white;
+}