feat(FN-3920): export repo override regex from github-tracking module

Exported the repo override regex from `@fusion/core` for use across packages, replacing an internal import in the dashboard's GitHub tracking component with the public API from core. Tests were updated in both packages to cover the new export.

Fusion-Task-Id: FN-3920

packages/dashboard/app/components/githubTracking.ts

@@ -1,6 +1,4 @@
-import type { GlobalSettings, ProjectSettings } from "@fusion/core";
-
-export const REPO_OVERRIDE_RE = /^[A-Za-z0-9._-]+\/[A-Za-z0-9._-]+$/;
+import { REPO_OVERRIDE_RE, type GlobalSettings, type ProjectSettings } from "@fusion/core";
 
 function normalizeRepoValue(value: string | null | undefined): string {
   const trimmed = value?.trim() ?? "";