fix(FN-3829): recover stale merging status and align chat sidebar search styling

- Add self-healing recovery for stale in-review merging statuses when no active merger owns the task
- Skip merge re-enqueue for tasks already marked with transient merging statuses and add regression coverage
- Wire active merge task ID provider through project runtime for safer stale-status detection
- Use chat-sidebar-search-container in ChatView with matching CSS padding
- Normalize fusion-plugin-reports test script to use local vitest and add changeset for @runfusion/fusion patch

Fusion-Task-Id: FN-3829

packages/engine/src/runtimes/in-process-runtime.ts

@@ -118,6 +118,7 @@ export class InProcessRuntime
    * before `start()` via `setMergeEnqueuer`.
    */
   private mergeEnqueuer?: (taskId: string) => void;
+  private activeMergeTaskIdProvider?: () => string | null;
   /** Tracks whether startup recovery was intentionally deferred due to pause state. */
   private startupRecoveryDeferred = false;
   /** Prevent duplicate unpause recovery dispatches from racing each other. */
@@ -621,6 +622,7 @@ export class InProcessRuntime
         getPlanningTaskIds: () => this.triageProcessor?.getProcessingTaskIds() ?? new Set<string>(),
         evictStaleTriageProcessing: () => this.triageProcessor?.evictStaleProcessing() ?? new Set<string>(),
         enqueueMerge: this.mergeEnqueuer ? (taskId: string) => this.mergeEnqueuer?.(taskId) : undefined,
+        getActiveMergeTaskId: () => this.activeMergeTaskIdProvider?.() ?? null,
       });
       this.selfHealingManager.start();
       this.stuckTaskDetector.start();
@@ -857,6 +859,10 @@ export class InProcessRuntime
     this.mergeEnqueuer = enqueueMerge;
   }
 
+  setActiveMergeTaskIdProvider(getActiveMergeTaskId: () => string | null): void {
+    this.activeMergeTaskIdProvider = getActiveMergeTaskId;
+  }
+
   /**
    * Resume executor/self-healing activity after an unpause transition.
    *