[changelog] Add changelog for java/v1.0.9

> [!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 the `java/v1.0.9` entry to `CHANGELOG.md` with 2 highlighted features and 9 other changes spanning Java-specific improvements and cross-SDK updates that landed in this release.

**Highlighted features:**
- `userPromptTransformed` hook via `SessionHooks.setOnUserPromptTransformed`
- Custom JSON schema override for `@CopilotToolParam` + compile-time blank-description enforcement

**Other changes (9):** disabled MCP servers, `agentStop` hook, `GitHubMcpToolConfig`, managed approval on permissions, `enableExperimentalMode`, additional directories, `customAgentsLocalOnly` forwarding, `ReasoningEffort.max`, and version-script bugfix.

> Generated by [Release Changelog Generator](https://github.com/github/copilot-sdk/actions/runs/31060734155) · sonnet46 70.5 AIC · ⌖ 9.03 AIC · ⊞ 8.6K · [◷](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-v1.0.9-0adf9c759a4da870': 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/31060734155)
>
> 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 31060734155 -n agent -D /tmp/agent-31060734155

# Fetch the bundle into a temporary ref, then update the local branch
git fetch /tmp/agent-31060734155/aw-changelog-java-v1.0.9.bundle refs/heads/changelog/java-v1.0.9:refs/bundles/create-pr-changelog-java-v1-0-9-0adf9c759a4da870-3276e03d
git update-ref refs/heads/changelog/java-v1.0.9-0adf9c759a4da870 refs/bundles/create-pr-changelog-java-v1-0-9-0adf9c759a4da870-3276e03d
git checkout changelog/java-v1.0.9-0adf9c759a4da870
# 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-v1-0-9-0adf9c759a4da870-3276e03d

# Push the branch to origin
git push origin changelog/java-v1.0.9-0adf9c759a4da870

# Create the pull request
gh pr create --title '[changelog] Add changelog for java/v1.0.9' --base main --head changelog/java-v1.0.9-0adf9c759a4da870 --repo github/copilot-sdk
```

查看生成的 changelog 详细信息以及 issue 中关于受保护文件的通知，然后下载 workflow 运行 31060734155 的 agent artifact。按照列出的 git 命令恢复 changelog 分支，并针对 main 创建 pull request。当 CHANGELOG.md 包含 java/v1.0.9 条目且提议的更改已提交以供审查时，即表示完成。

由索引模型根据 Issue 内容生成。