docs: update changelog for v0.27.1

[augmentmoogi]

Update v0.27.1 release notes to document the new built-in general-purpose sub-agent.

• Describe support for a built-in general-purpose sub-agent designed for deep research, code search, and multi-step workflows.
• Capture the release impact so reviewers and users can quickly understand what was introduced in v0.27.1.

---

🤖 This description was generated automatically. Please react with 👍 if it's helpful or 👎 if it needs improvement.

[augmentmoogi]

👋 This PR is being monitored by an automated agent. Here's what I can do:

• Answer questions about the changelog changes
• Implement suggestions if you request formatting or content changes
• Fix merge conflicts if the PR falls behind main
• Merge the PR once a human has approved it

I check in every 5 minutes. Any new comment will wake me up.

[github-actions]

Thanks for updating the release notes. I left one documentation consistency comment to help keep the changelog aligned with published stable versions.

---

🤖 Automated review complete. Please react with 👍 or 👎 on the individual review comments to provide feedback on their usefulness.

[github-actions]

Because this new top entry now jumps straight from 0.27.1 to 0.25.1, the changelog reads as if stable releases 0.26.0 and 0.27.0 never happened, but both tags already exist in the repo. Could we add those missing sections (or otherwise clarify why they’re intentionally omitted) so users aren’t missing two stable releases worth of notes?

[augmentmoogi]

👋 This PR is being monitored by an automated agent. Here's what I can do:

• Answer questions about the changelog changes
• Implement suggestions if you request formatting or content changes
• Fix merge conflicts if the PR falls behind main
• Merge the PR once a human has approved it

I check in every 5 minutes. Any new comment will wake me up.

[augment-app-staging]

^{PR Risk Analyzer Agent🛡️}

Risk Analysis 🛡️ · Low Risk

✅ Approved — Low-Risk Change

Details

Documentation-only change: 5 additions, 0 deletions to `CHANGELOG.md`, adding a v0.27.1 "New Features" entry for a built-in general-purpose sub-agent. No code, tests, config, schema, infra, or AI-prompt changes — nothing that can affect runtime behavior.

Memory (seen 2×; last PR-133; permanent): the public CHANGELOG.md must list only user-facing CLI features. The added entry describes a user-facing CLI sub-agent capability and is not internal tooling, the experimental auggie cloud group, or a Cosmos/expert-builder change, so it satisfies that rule.

[augment-app-staging]

^{Deep Code Review Agent🐛}

Review completed with 1 suggestions.

[augment-app-staging]

This 0.27.1 entry documents adding a built-in general-purpose sub-agent, but the 0.28.0 section just above also lists "General-Purpose Subagent: Added a built-in general-purpose subagent option," so the same feature now appears as newly added in two releases; could you confirm which release actually introduced it and remove or reword the duplicate?

Severity: medium

---

_{🤖 Was this useful? React with 👍 or 👎}