Prepare 0.4.0 release

[hiyouga]

Bump the version to 0.4.0 and turn the top changelog entry into the release line.

0.4.0 ships the fidelity content-item payload that replaces the per-item signature/phase fields (breaking — histories recorded by 0.3.x need those fields moved under fidelity to replay, see the details file), and OpenAI-compatible clients now replay thinking through exactly the reasoning field the upstream produced. The minor bump follows from the breaking data-model change.

• src_py/pyproject.toml: 0.3.3 → 0.4.0
• src_ts/package.json / package-lock.json: 0.3.3 → 0.4.0
• CHANGELOG.md: release line for 0.4.0

🤖 Generated with Claude Code

https://claude.ai/code/session_01J8bNMvyPJ7muyDs4Fh9ZLF

[Copilot]

Pull request overview

Prepares the AgentHub 0.4.0 release by bumping published package versions (Python + TypeScript) and promoting the top changelog entry into an explicit 0.4.0 release line, aligning with the breaking fidelity payload/data-model change described in the linked details doc.

Changes:

• Bump Python package version from 0.3.3 to 0.4.0 (src_py/pyproject.toml).
• Bump TypeScript package version from 0.3.3 to 0.4.0 (src_ts/package.json and src_ts/package-lock.json).
• Update CHANGELOG.md top entry to include “Release version 0.4.0 …” while preserving the details link.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
src_ts/package.json	Updates npm package version to 0.4.0 for the release.
src_ts/package-lock.json	Keeps lockfile metadata aligned with the 0.4.0 package version.
src_py/pyproject.toml	Updates Python package version to 0.4.0 for the release.
CHANGELOG.md	Converts the top changelog item into the explicit 0.4.0 release line and keeps the details reference.

Files not reviewed (1)

• src_ts/package-lock.json: Generated file