fix(nc): enable Nextcloud Android app connectivity and uploads

- Add /remote.php/dav discovery endpoint for Android app server detection
- Add /index.php/204 connectivity check endpoint (returns 204 No Content)
- Redirect login flow to nc:// deep link for mobile credential delivery
- Support GET/HEAD on folders (NC clients use as existence checks)
- Recursive MKCOL to create missing parent directories
- Fix single-file PROPFIND returning empty multistatus response
- Strip instance suffix from preview fileId (e.g. "00000326ocnca")
- Add recommendations stub endpoint

src/interfaces/nextcloud/ocs_handler.rs

@@ -229,6 +229,19 @@ pub async fn handle_notifications_push() -> Response {
     Json(ocs_ok(200, json!({}))).into_response()
 }
 
+/// GET /ocs/v2.php/apps/recommendations/api/v1/recommendations
+///
+/// Returns recommended files. Stub that returns an empty list.
+pub async fn handle_recommendations() -> Response {
+    Json(json!({
+        "ocs": {
+            "meta": { "status": "ok", "statuscode": 200, "message": "OK" },
+            "data": []
+        }
+    }))
+    .into_response()
+}
+
 /// GET /ocs/v2.php/apps/files_sharing/api/v1/sharees?search={query}&itemType={type}
 ///
 /// Returns matching users for the sharing autocomplete UI.