chore(release): prepare release v0.4.0

[vertefra]

Release v0.4.0

This PR prepares the release of version 0.4.0.

Changes Summary

• Version bump: Updated VERSION file from 0.3.1 to 0.4.0
• New PostgreSQL tool: Added comprehensive PostgreSQL tool with query execution, validation, and schema operations
• Agent improvements: Enhanced agent chat functionality and configuration handling
• Builder enhancements: Improved agent builder with better tool support and documentation
• Testing: Added comprehensive test coverage for agents, history, and plugins
• Documentation: Updated builder README with detailed configuration guide

Testing

• ✅ All unit tests passing
• ✅ Linting and formatting checks passing
• ✅ Code coverage maintained

Files Changed

40 files changed, 3538 insertions(+), 86 deletions(-)

Next Steps

After merge:

1. Tag the release: git tag v0.4.0
2. Push tag: git push origin v0.4.0
3. GitHub Actions will automatically create the release

[github-actions]

Version Check Results

✅ Version format is valid: 0.4.0

The VERSION file has been updated. Please ensure this matches the intended release version.

[github-actions]

Version Check Results

✅ Version format is valid: 0.4.0

The VERSION file has been updated. Please ensure this matches the intended release version.