fix: handle null comment/review author from deleted accounts (#1490)

GitHub's GraphQL author field is null when the account behind a
comment, review, PR, or issue has been deleted (the ghost user). The
action typed author as non-null and read author.login directly, so a
single comment from a deleted account threw and was swallowed into a
generic 'Failed to fetch PR/issue data', failing the entire run.

Make author nullable on the four affected types and fall back to
'ghost' at each login read. With the type nullable, tsc flags every
dereference, so all sites are covered.

test/data-fetcher.test.ts

@@ -1499,4 +1499,42 @@ describe("filterCommentsByActor", () => {
     const filtered = filterCommentsByActor(comments, "user1", "");
     expect(filtered).toHaveLength(0);
   });
+
+  test("does not crash on comments from deleted (null-author) accounts", () => {
+    // GitHub's GraphQL returns author: null for comments whose account was
+    // deleted. With an exclude filter set (the exact `*[bot]` config we
+    // recommend), the null author must not throw when dereferenced.
+    const comments = [
+      { author: { login: "user1" }, body: "comment1" },
+      { author: null, body: "from a deleted account" },
+      { author: { login: "bot[bot]" }, body: "comment3" },
+    ];
+
+    const { filterCommentsByActor } = require("../src/github/data/fetcher");
+    const filtered = filterCommentsByActor(comments, "", "*[bot]");
+    // ghost comment is retained (it matches no exclude pattern); the bot is dropped.
+    expect(filtered).toHaveLength(2);
+    expect(filtered.map((c: any) => c.body)).toEqual([
+      "comment1",
+      "from a deleted account",
+    ]);
+  });
+
+  test("treats null author as the 'ghost' login for include/exclude", () => {
+    const comments = [
+      { author: null, body: "from a deleted account" },
+      { author: { login: "user1" }, body: "comment2" },
+    ];
+
+    const { filterCommentsByActor } = require("../src/github/data/fetcher");
+    // Excluding "ghost" removes the deleted-account comment.
+    expect(filterCommentsByActor(comments, "", "ghost")).toHaveLength(1);
+    expect(filterCommentsByActor(comments, "", "ghost")[0].body).toBe(
+      "comment2",
+    );
+    // Including only "ghost" keeps just the deleted-account comment.
+    const onlyGhost = filterCommentsByActor(comments, "ghost", "");
+    expect(onlyGhost).toHaveLength(1);
+    expect(onlyGhost[0].body).toBe("from a deleted account");
+  });
 });