feat: render thinking process UI for intermediate agent messages

Wire message-reclassified sidecar events through the main process to
the renderer, where reclassified messages are filtered out of the main
transcript and collected into a collapsible ThinkingProcess component.

Main process changes:
- Route message-reclassified via dedicated onMessageReclassified callback
- Add applyMessageReclassified handler that sets messageKind and emits
  the session event for the renderer
- Forward assistant-intent and reasoning-delta as turn-scoped events

Renderer changes:
- Split session.messages into visibleMessages and thinkingMessages
- Render ThinkingProcess above the last assistant message
- ThinkingProcess auto-expands during active turns, collapses on finish
- Update messagePhase to skip thinking-kind messages for final detection

Tests:
- 3 new sessionWorkspace tests for reclassification apply/dedup/ignore
- 2 new messagePhase tests for thinking-kind handling
- Updated runTurnPending test fixtures for new callback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/AryxAppService.ts

@@ -10,6 +10,7 @@ import type {
   ExitPlanModeRequestedEvent,
   MessageMode,
   McpOauthRequiredEvent,
+  MessageReclassifiedEvent,
   RunTurnCustomAgentConfig,
   RunTurnToolingConfig,
   SidecarCapabilities,
@@ -1364,6 +1365,9 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
         async (event) => {
           await this.handleExitPlanModeRequested(workspace, session.id, event);
         },
+        async (event) => {
+          await this.applyMessageReclassified(workspace, session.id, event);
+        },
         async (event) => {
           await this.handleTurnScopedEvent(workspace, session.id, event);
         },
@@ -1715,6 +1719,31 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     }
   }
 
+  private async applyMessageReclassified(
+    workspace: WorkspaceState,
+    sessionId: string,
+    event: MessageReclassifiedEvent,
+  ): Promise<void> {
+    const session = this.requireSession(workspace, sessionId);
+    const message = session.messages.find((m) => m.id === event.messageId);
+    if (!message || message.messageKind === 'thinking') {
+      return;
+    }
+
+    message.messageKind = 'thinking';
+    const occurredAt = nowIso();
+    session.updatedAt = occurredAt;
+    await this.workspaceRepository.save(workspace);
+
+    this.emitSessionEvent({
+      sessionId,
+      kind: 'message-reclassified',
+      occurredAt,
+      messageId: event.messageId,
+      messageKind: 'thinking',
+    });
+  }
+
   private async applyAgentActivity(
     workspace: WorkspaceState,
     sessionId: string,