[changelog] Add changelog for java/v1.0.8

> [!CAUTION]
> Protected files were modified in this change.
> This pull request is in `request_review` mode and requires explicit human scrutiny before merge.
>
> Protected files: `CHANGELOG.md`

Adds CHANGELOG.md entry for the java/v1.0.8 release (2 user-facing changes: per-agent reasoning effort and strongly-typed expAssignments).

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `awmgmcpg`
>> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "awmgmcpg"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [Release Changelog Generator](https://github.com/github/copilot-sdk/actions/runs/29965619881) · 44.4 AIC · ⌖ 5.53 AIC · ⊞ 7.2K · [◷](https://github.com/search?q=repo%3Agithub%2Fcopilot-sdk+%22gh-aw-workflow-id%3A+release-changelog%22&type=pullrequests)

---

> [!NOTE]
> This was originally intended as a pull request, but the git push operation failed.
>
> **Original error:** pushSignedCommits: refusing unsigned push for branch 'changelog/java-v1.0.8-e1e3ac881ac8d09a': Signed-commit payload violates file-protection policy (request_review): CHANGELOG.md
>
> **Workflow Run:** [View run details and download bundle artifact](https://github.com/github/copilot-sdk/actions/runs/29965619881)
>
> The bundle file is available in the `agent` artifact in the workflow run linked above.

To create a pull request with the changes:

```sh
# Download the artifact from the workflow run
gh run download 29965619881 -n agent -D /tmp/agent-29965619881

# Fetch the bundle into a temporary ref, then update the local branch
git fetch /tmp/agent-29965619881/aw-changelog-java-v1.0.8.bundle refs/heads/changelog/java-v1.0.8:refs/bundles/create-pr-changelog-java-v1-0-8-e1e3ac881ac8d09a-acc663cb
git update-ref refs/heads/changelog/java-v1.0.8-e1e3ac881ac8d09a refs/bundles/create-pr-changelog-java-v1-0-8-e1e3ac881ac8d09a-acc663cb
git checkout changelog/java-v1.0.8-e1e3ac881ac8d09a
# Ensure the working tree matches the updated branch
git reset --hard
# Remove the temporary bundle ref
git update-ref -d refs/bundles/create-pr-changelog-java-v1-0-8-e1e3ac881ac8d09a-acc663cb

# Push the branch to origin
git push origin changelog/java-v1.0.8-e1e3ac881ac8d09a

# Create the pull request
gh pr create --title '[changelog] Add changelog for java/v1.0.8' --base main --head changelog/java-v1.0.8-e1e3ac881ac8d09a --repo github/copilot-sdk
```

Bắt đầu với CHANGELOG.md và lần chạy workflow Release Changelog Generator được liên kết. Tải artifact `agent` xuống và kiểm tra `aw-changelog-java-v1.0.8.bundle` trước khi áp dụng hoặc tạo lại branch. Công việc được xem là hoàn tất khi CHANGELOG.md chứa mục java/v1.0.8 bao quát nỗ lực suy luận cho từng agent và expAssignments được định kiểu mạnh, sau đó là pull request được yêu cầu.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.