[changelog] Add changelog for v1.0.11

> [!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 `v1.0.11` changelog entry to `CHANGELOG.md`.

Covers 6 highlighted features and 4 other changes across all SDKs, plus 3 new contributors.

> Generated by [Release Changelog Generator](https://github.com/github/copilot-sdk/actions/runs/31818422729) · sonnet46 39.5 AIC · ⌖ 9.24 AIC · ⊞ 8.1K · [◷](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/v1.0.11-47e41bc8a651a7bc': 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/31818422729)
>
> 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 31818422729 -n agent -D /tmp/agent-31818422729

# Fetch the bundle into a temporary ref, then update the local branch
git fetch /tmp/agent-31818422729/aw-changelog-v1.0.11.bundle refs/heads/changelog/v1.0.11:refs/bundles/create-pr-changelog-v1-0-11-47e41bc8a651a7bc-d2cf7a75
git update-ref refs/heads/changelog/v1.0.11-47e41bc8a651a7bc refs/bundles/create-pr-changelog-v1-0-11-47e41bc8a651a7bc-d2cf7a75
git checkout changelog/v1.0.11-47e41bc8a651a7bc
# 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-v1-0-11-47e41bc8a651a7bc-d2cf7a75

# Push the branch to origin
git push origin changelog/v1.0.11-47e41bc8a651a7bc

# Create the pull request
gh pr create --title '[changelog] Add changelog for v1.0.11' --base main --head changelog/v1.0.11-47e41bc8a651a7bc --repo github/copilot-sdk
```

Start with CHANGELOG.md and the linked Release Changelog Generator workflow run. Download the agent artifact, fetch and check out the generated changelog branch using the documented git commands, then verify the changelog entry before pushing the branch and opening the pull request described in the issue.

索引モデルが issue の本文から書いたものです。