fix(agent): allow no-repo cloud runs to clone repos

[tatoalo]

Problem

Slack-origin cloud runs can start without a repository, but still have GitHub credentials injected for the linked user. In that state, users can ask the agent to clone a repo, but the no-repository prompt currently forbids branch, commit, and PR operations even after the repo is cloned.

We do need a proper repo injection but this will do for now.

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
packages/agent/src/server/agent-server.test.ts:613-644
**Prefer parameterised tests**

The two new tests cover the same feature (no-repository mode prompt content) across two `createPr` values. The team's coding standard prefers `it.each` for cases like this, keeping expectations DRY and making it easy to add a third case later (e.g. explicit `createPr: true`).

```ts
it.each([
  {
    label: "createPr unset (permissive)",
    config: { repositoryPath: undefined },
    shouldContain: [
      "Cloud Task Execution — No Repository Mode",
      "Clone the repository into /tmp/workspace/repos/<owner>/<repo>",
      "gh repo clone <owner>/<repo> /tmp/workspace/repos/<owner>/<repo>",
      "If the user explicitly asks you to open or update a pull request",
      "open a draft pull request",
      "unless the user explicitly asks",
      "Generated-By: PostHog Code",
      "Task-Id: test-task-id",
    ],
    shouldNotContain: [],
  },
  {
    label: "createPr false (restricted)",
    config: { repositoryPath: undefined, createPr: false },
    shouldContain: [
      "Cloud Task Execution — No Repository Mode",
      "You may clone a repository and make local edits in that clone",
      "Do NOT create branches, commits, push changes, or open pull requests in this run",
    ],
    shouldNotContain: ["open a draft pull request", "gh pr create --draft"],
  },
])(
  "no-repository mode: $label",
  ({ config, shouldContain, shouldNotContain }) => {
    const s = createServer(config);
    const prompt = (s as unknown as TestableServer).buildCloudSystemPrompt();
    for (const text of shouldContain) expect(prompt).toContain(text);
    for (const text of shouldNotContain) expect(prompt).not.toContain(text);
  },
);
```

_{Reviews (1): Last reviewed commit: "fix(agent): allow no-repo cloud runs to ..." | Re-trigger Greptile}