chore(release): prepare 0.4.0

[ramonlimaramos]

Summary

• bump Synapto package version to 0.4.0
• document 0.4.0 release notes for incremental MCP memory updates and dependency audit fixes
• update uv.lock for the 0.4.0 package version, PyJWT 2.13.0, and pip 26.1.2

Includes

• PR feat(mcp): add incremental memory updates #52: feat(mcp): add incremental memory updates
• PR fix(security): bump vulnerable transitive deps #53: fix(security): bump vulnerable transitive deps
• additional audit constraints for current pip-audit advisories: PyJWT>=2.13.0 and pip>=26.1.2

Validation

• uv run ruff check src/ tests/
• uv run python -c 'import synapto; print(synapto.version)'
• uv run bandit -r src/synapto/ -c pyproject.toml
• uv sync --extra dev --python 3.13
• uv run pip-audit
• uv run pytest tests/ -q
• git diff --check
• uv run python -m build

After this PR merges, run the release workflow with bump_type=current.