FN-5677: add per-task auto-merge override controls

Add dashboard and API support to set or clear per-task auto-merge overrides during review.

- add TaskReviewTab UI controls and styles for selecting or clearing an auto-merge override
- wire legacy dashboard API request handling for task auto-merge override updates
- update task workflow routes to persist override operations
- add dashboard and route tests covering set/clear override behavior

Files changed:
 packages/dashboard/app/__tests__/api-tasks.test.ts | 26 +++++++++
 packages/dashboard/app/api/legacy.ts               |  1 +
 packages/dashboard/app/components/TaskReviewTab.css     | 17 ++++++
 packages/dashboard/app/components/TaskReviewTab.tsx     | 55 +++++++++++++++++-
 packages/dashboard/app/components/__tests__/TaskReviewTab.test.tsx    | 48 ++++++++++++++++
 packages/dashboard/src/__tests__/routes-tasks-ops.test.ts         | 65 ++++++++++++++++++++++
 packages/dashboard/src/routes/register-task-workflow-routes.ts    |  7 ++-
 7 files changed, 216 insertions(+), 3 deletions(-)

Fusion-Task-Id: FN-5677

Fusion-Task-Lineage: 4503e605-1190-4a32-8736-dd11eb2756b8

packages/dashboard/app/components/TaskReviewTab.css

@@ -48,6 +48,14 @@
 .task-review-tab__actions {
   display: flex;
   gap: var(--space-sm);
+  align-items: flex-start;
+}
+
+.task-review-tab__auto-merge-control {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-2xs);
+  min-inline-size: max-content;
 }
 
 .task-review-tab__list {
@@ -179,6 +187,15 @@
     flex-wrap: wrap;
   }
 
+  .task-review-tab__auto-merge-control {
+    width: 100%;
+    min-inline-size: 0;
+  }
+
+  .task-review-tab__auto-merge-control .select {
+    width: 100%;
+  }
+
   .task-review-tab__refresh-meta {
     align-items: flex-start;
   }