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/api/legacy.ts

@@ -454,6 +454,7 @@ export function updateTask(
     reviewLevel?: number | null;
     executionMode?: "standard" | "fast" | null;
     noCommitsExpected?: boolean;
+    autoMerge?: boolean | null;
     priority?: TaskPriority | null;
     sourceIssue?: TaskSourceIssue | null;
     nodeId?: string | null;