Incorrect push_rules endpoint for notifications

[Proxymiity]

Describe the bug

When changing notification settings, the setting doesn't change because Cinny tries to post data to /_matrix/client/v3/user/.../account_data/m.push_rules, which apparently is not supported by Synapse.

Reproduction

1. Open Cinny (Dev or Stable)
2. Go to Settings
3. Go to the "Notifications" tab
4. Change any of the Global Notification settings
5. Case a: it changes locally, but is only visual -- Case b: it does not change at all

Expected behavior

The notification setting should apply correctly (Element Stable does work correctly with /pushrules, not /m.push_rules)

Platform and versions

Tested on:
1. OS: macOS 15
2. Browser: Firefox Nightly 133.0a1
3. Cinny version: v4.2.2 (dev.cinny.in) 
4. Homeserver: nya.network (matrix.nya.network) -> Synapse v1.117.0

Tested on:
1. OS: macOS 15
2. Cinny version: v4.2.2 (app, stable)
3. Homeserver: nya.network (matrix.nya.network) -> Synapse v1.117.0

Additional context

No response