fix CRITICAL: add missing ReasoningTokenEvent interface + union variant

REASONING_TOKEN was declared in the ExecutionEventType union (line 22) and
yielded from AgentExecutor.ts (lines 174, 388), but no ReasoningTokenEvent
interface existed and it was not in the ExecutionEvent discriminated union
(lines 525-574). This caused TypeScript to flag type errors when yielding
these events and made ExecutionSessionManager.ts:1110 rely on 'any' coercion.

Added interface with type: 'REASONING_TOKEN', executionId, token, timestamp.

Author: patil-shubham-dev

apps/desktop/src/renderer/runtime/ExecutionEvent.ts

@@ -212,6 +212,13 @@ export interface TokenEvent {
   timestamp: number
 }
 
+export interface ReasoningTokenEvent {
+  type: "REASONING_TOKEN"
+  executionId: string
+  token: string
+  timestamp: number
+}
+
 export interface FallbackActivatedEvent {
   type: "FALLBACK_ACTIVATED"
   executionId: string
@@ -541,6 +548,7 @@ export type ExecutionEvent =
   | (ProviderConnectingEvent & ExecutionTraceable)
   | (ProviderConnectedEvent & ExecutionTraceable)
   | (TokenEvent & ExecutionTraceable)
+  | (ReasoningTokenEvent & ExecutionTraceable)
   | (MessageUpdateEvent & ExecutionTraceable)
   | (MessageCompleteEvent & ExecutionTraceable)
   | (ExecutionCompleteEvent & ExecutionTraceable)