feat: defer remote branch creation until first commit (#244)

* feat: defer remote branch creation until first commit

- For commit signing: branches are created remotely by github-file-ops-server on first commit
- For non-signing: branches are created locally with 'git checkout -b' and pushed when needed
- Consolidated duplicate branch creation logic in github-file-ops-server into a shared helper function
- Claude is unaware of these implementation details and simply sees it's on the correct branch
- No branch links are shown in initial comments since branches don't exist remotely yet

* fix: prevent broken branch links in final comment update

- Check if branch exists remotely before adding branch link
- Only add branch links for branches that actually exist on GitHub
- Add test coverage for non-existent remote branches
- Fixes issue where users would see broken branch links for local-only branches

* fix: don't show branch name in comment header when branch doesn't exist remotely

- Only pass branchName to updateCommentBody when branchLink exists
- Prevents showing branch names for branches that only exist locally
- Add test to verify branch name is not shown when branch doesn't exist

* tmp

test/comment-logic.test.ts

@@ -1,5 +1,8 @@
 import { describe, it, expect } from "bun:test";
-import { updateCommentBody } from "../src/github/operations/comment-logic";
+import {
+  updateCommentBody,
+  type CommentUpdateInput,
+} from "../src/github/operations/comment-logic";
 
 describe("updateCommentBody", () => {
   const baseInput = {
@@ -417,5 +420,27 @@ describe("updateCommentBody", () => {
         "• [Create PR ➔](https://github.com/owner/repo/compare/main...claude/issue-123-20240101_120000)",
       );
     });
+
+    it("should not show branch name when branch doesn't exist remotely", () => {
+      const input: CommentUpdateInput = {
+        currentBody: "@claude can you help with this?",
+        actionFailed: false,
+        executionDetails: { duration_ms: 90000 },
+        jobUrl: "https://github.com/owner/repo/actions/runs/123",
+        branchLink: "", // Empty branch link means branch doesn't exist remotely
+        branchName: undefined, // Should be undefined when branchLink is empty
+        triggerUsername: "claude",
+        prLink: "",
+      };
+
+      const result = updateCommentBody(input);
+
+      expect(result).toContain("Claude finished @claude's task in 1m 30s");
+      expect(result).toContain(
+        "[View job](https://github.com/owner/repo/actions/runs/123)",
+      );
+      expect(result).not.toContain("claude/issue-123");
+      expect(result).not.toContain("tree/claude/issue-123");
+    });
   });
 });