Update changelogs from fern repo (#4383)

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2026-03-19.mdx

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+## 2.35.0
+**`(fix):`** Fix WebSocket binary message sending. Binary messages (e.g. audio bytes) are now
+sent as raw bytes instead of being JSON-serialized, which caused servers to reject
+them with CONFIG_DENIED.
+
+
+**`(fix):`** Fix WebSocket incoming message deserialization. `TryDeserialize` now passes
+`JsonSerializerOptions` so the generated literal property setters correctly
+validate const discriminator fields (e.g. `type: "transcript"` vs `type: "flushed"`)
+during deserialization.
+
+
+**`(feat):`** Add forward-compatible `UnknownMessage` event to WebSocket clients. When the server
+sends an event type not recognized by the SDK, it is now dispatched to the
+`UnknownMessage` event handler (as a `JsonElement`) instead of raising an exception.
+This allows SDKs to gracefully handle new server event types without requiring
+regeneration.
+
+