feat(FN-3874): add GitHub tracking to task creation and detail views

Adds GitHub tracking to the task system across create, detail, and patch flows: the NewTaskModal gains GitHub tracking controls (Step 1), TaskDetailModal gets a new UI section for viewing and editing GitHub repo/issue links (Step 2), and the task workflow API routes gain a PATCH handler wired throug

Fusion-Task-Id: FN-3874

packages/core/src/github-tracking.ts

@@ -1,5 +1,7 @@
 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 interface RepoSlug {
   owner: string;
   repo: string;

packages/core/src/index.ts

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