fix: detect identity reset by listening to cross-signing key changes (#1258)

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### Description

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relevant motivation and context. List any dependencies that are required
for this change. -->

When the server/IdP resets identity, the Matrix SDK fires
CryptoEvent.KeysChanged, but the client only re-evaluated verification
status on CryptoEvent.DevicesUpdated. So after a reset the client kept
showing "Verified" and never surfaced the unverified state.
Adds useCrossSigningKeysChange (mirroring useDeviceListChange) and wires
it into both verification hooks so status and unverified-device count
re-evaluate on key changes. The existing unverified banner and Devices
page then reflect the reset.

Fixes #1255

#### Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update

### Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings

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Author: 7w1

src/app/hooks/useDeviceVerificationStatus.ts

@@ -1,11 +1,23 @@
 import { useCallback, useEffect, useState } from 'react';
-import type { CryptoApi } from '$types/matrix-sdk';
+import { type CryptoApi, type CryptoEventHandlerMap, CryptoEvent } from '$types/matrix-sdk';
 import { verifiedDevice } from '$utils/matrix-crypto';
 import { fulfilledPromiseSettledResult } from '$utils/common';
 import { useAlive } from './useAlive';
 import { useMatrixClient } from './useMatrixClient';
 import { useDeviceListChange } from './useDeviceList';
 
+export const useCrossSigningKeysChange = (
+  onChange: CryptoEventHandlerMap[CryptoEvent.KeysChanged]
+) => {
+  const mx = useMatrixClient();
+  useEffect(() => {
+    mx.on(CryptoEvent.KeysChanged, onChange);
+    return () => {
+      mx.removeListener(CryptoEvent.KeysChanged, onChange);
+    };
+  }, [mx, onChange]);
+};
+
 export enum VerificationStatus {
   Unknown,
   Unverified,
@@ -48,6 +60,8 @@ export const useDeviceVerificationDetect = (
       [userId, updateStatus]
     )
   );
+
+  useCrossSigningKeysChange(useCallback(() => updateStatus(), [updateStatus]));
 };
 
 export const useDeviceVerificationStatus = (
@@ -98,6 +112,8 @@ export const useUnverifiedDeviceCount = (
     )
   );
 
+  useCrossSigningKeysChange(useCallback(() => updateCount(), [updateCount]));
+
   useEffect(() => {
     updateCount();
   }, [updateCount]);