Update commit on branch refresh and validate commit exists on save

Refresh button now always updates the commit to the latest SHA instead
of preserving the stale one in edit mode. Both create and update routes
verify the commit still exists on GitHub before persisting.

src/server/routes/repository-private.ts

@@ -431,6 +431,11 @@ router.post(
           httpStatus: 404,
         });
       }
+
+      await repository.getCommitInfo(repoUpdate.source.commit, {
+        accessToken: user.accessToken,
+      });
+
       const removeRepoFromConference = async (conferenceID: string) => {
         const conf = await ConferenceModel.findOne({
           conferenceID,
@@ -542,6 +547,10 @@ router.post("/", async (req: express.Request, res: express.Response) => {
       });
     }
 
+    await repository.getCommitInfo(repoUpdate.source.commit, {
+      accessToken: user.accessToken,
+    });
+
     const repo = new AnonymizedRepositoryModel();
     repo.repoId = repoUpdate.repoId;
     repo.anonymizeDate = new Date();