Potential ANR / main-thread blocking risk

## Environment

- App: Nextcloud Dev (`com.nextcloud.android.beta`)
- Branch checked: `master`
- File: `app/src/main/java/third_parties/sufficientlysecure/ProcessVEvent.java`:169
- Verified commit: `b716c74d97c5ac9e74c6047ba3a9e5884977a729`

### The Issue

While reviewing `SyncedFolderProvider.getSyncedFolders() → ContentResolver-query`, I noticed a potential main-thread blocking risk around `android.content.ContentResolver#query(android.net.Uri,java.lang.String[],java.lang.String,java.lang.String[],java.lang.String)`.

The latest source still operates synchronously:

```java
166: // Determine if we need to delete a duplicate event in order to update it
167: if (!mustDelete && dupes != DuplicateHandlingEnum.DUP_DONT_CHECK) {
168:
169: cur = query(resolver, options, c);
170: while (!mustDelete && cur != null && cur.moveToNext()) {
171: if (dupes == DuplicateHandlingEnum.DUP_REPLACE) {
172: mustDelete = cur.getLong(EVENT_QUERY_CALENDAR_ID_COL) == selectedCal.mId;
173: } else {
174: mustDelete = true; // Replacing all (or ignoring, handled just below)
```

`android.content.ContentResolver#query(android.net.Uri,java.lang.String[],java.lang.String,java.lang.String[],java.lang.String)` can block the calling thread while Android resolves a provider, opens a stream, performs database work, contacts account services, touches storage, or waits on remote I/O, depending on the API and URI/backend involved.

### The Risk & Impact

If this method is reached from a UI-thread path, the operation can cause visible jank, StrictMode violations in debug builds, or an ANR when the provider/backend is slow, blocked, or unreachable. I am phrasing this as a source-level risk because I verified the current source pattern but did not run an on-device reproduction.

### Current source path

```text

-> android.content.ContentResolver#query(android.net.Uri,java.lang.String[],java.lang.String,java.lang.String[],java.lang.String)
```

### Verification

I checked the latest upstream source at `b716c74d97c5ac9e74c6047ba3a9e5884977a729` and found the sensitive operation still present in `app/src/main/java/third_parties/sufficientlysecure/ProcessVEvent.java`. This report is based on source-level inspection, not runtime reproduction.

### Expected behaviour

Move this method call to a worker thread instead. Please refer to https://developer.android.com/studio/write/annotations#thread-annotations for more details.

### Actual behaviour

The method call is conducted on the main thread, causing potential ANR or response-related performance issues.