feat(FN-3918): restore github tracking regex helper and tests

Restores a local GitHub tracking regex helper in the dashboard and adds regression tests to prevent future regressions. The feature restores functionality that was previously removed, with tests covering the helper's behavior.

Fusion-Task-Id: FN-3918

packages/dashboard/app/components/__tests__/githubTracking.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from "vitest";
+import { REPO_OVERRIDE_RE, resolveEffectiveGithubRepoDefault } from "../githubTracking";
+
+describe("githubTracking helper", () => {
+  it("accepts valid owner/repo values and rejects malformed values", () => {
+    expect(REPO_OVERRIDE_RE.test("owner/repo")).toBe(true);
+    expect(REPO_OVERRIDE_RE.test("org.name/repo_name-1")).toBe(true);
+
+    expect(REPO_OVERRIDE_RE.test("owner")).toBe(false);
+    expect(REPO_OVERRIDE_RE.test("owner/repo/extra")).toBe(false);
+    expect(REPO_OVERRIDE_RE.test("owner repo/repo")).toBe(false);
+    expect(REPO_OVERRIDE_RE.test(" owner/repo ")).toBe(false);
+  });
+
+  it("prefers project repo, then global repo, then empty string", () => {
+    expect(
+      resolveEffectiveGithubRepoDefault(
+        { githubTrackingDefaultRepo: "project/repo" },
+        { githubTrackingDefaultRepo: "global/repo" },
+      ),
+    ).toBe("project/repo");
+
+    expect(
+      resolveEffectiveGithubRepoDefault(
+        { githubTrackingDefaultRepo: "  " },
+        { githubTrackingDefaultRepo: "global/repo" },
+      ),
+    ).toBe("global/repo");
+
+    expect(resolveEffectiveGithubRepoDefault({}, {})).toBe("");
+  });
+});