feat(FN-3929): dedupe REPO_OVERRIDE_RE export from core

Cleaned up a duplicate export of `REPO_OVERRIDE_RE` from the core package index, removing the redundant declaration from `packages/core/src/index.ts` while keeping it defined in `github-tracking.ts` where it logically belongs.

Fusion-Task-Id: FN-3929

packages/core/src/github-tracking.ts

@@ -1,6 +1,6 @@
 import { REPO_OVERRIDE_RE, type GlobalSettings, type ProjectSettings, type Task } from "./types.js";
 
-export const REPO_OVERRIDE_RE = /^[A-Za-z0-9._-]+\/[A-Za-z0-9._-]+$/;
+export { REPO_OVERRIDE_RE };
 
 export interface RepoSlug {
   owner: string;

packages/core/src/index.ts

@@ -109,7 +109,6 @@ export {
   type GhError,
 } from "./gh-cli.js";
 export {
-  REPO_OVERRIDE_RE,
   parseRepoSlug,
   isValidRepoSlug,
   resolveTaskGithubTracking,