FN-6016: quarantine flaky chat-manager generation-slot test

Quarantine the flaky dashboard chat-manager generation-slot test until the underlying race is fixed.

- exclude packages/dashboard/src/__tests__/chat-manager.test.ts from dashboard API Vitest projects
- record the quarantine entry with failure context, rescue requirements, and the 2026-06-08 quarantine date

Files changed:
 packages/dashboard/vitest.config.ts | 2 ++
 scripts/lib/test-quarantine.json    | 8 +++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

Fusion-Task-Id: FN-6016

Fusion-Task-Lineage: 2cd97f8e-db06-4e49-b437-66fee64fb3a9

packages/dashboard/vitest.config.ts

@@ -258,6 +258,7 @@ const qualityAppBackfillTests = ["app/**/*.test.{ts,tsx}"];
 const backfillApiExclude = [
   ...qualityApiTests,
   ...skipListDashboardGlobs.filter((file) => file.startsWith("src/")),
+  "src/__tests__/chat-manager.test.ts",
 ];
 const qualityApiBackfillTests = ["src/**/*.test.{ts,tsx}"];
 
@@ -449,6 +450,7 @@ export default defineConfig({
           name: "dashboard-api",
           environment: "node",
           include: ["src/**/*.test.{ts,tsx}"],
+          exclude: ["src/__tests__/chat-manager.test.ts"],
           css: { include: [] },
         },
       },