chore(release): 0.4.0

[daniel3303]

Summary

• Cuts the 0.4.0 release: moves the ReadOnly-hardening and security-review changes from fix: harden ReadOnly SQL validation and fix security-review findings #154 into a dated changelog section (Security / Changed / Fixed), and repairs the missing 0.3.0 comparison link.

Code changes

• CHANGELOG.md — adds the [0.4.0] — 2026-07-07 section and updates the comparison links at the bottom (adds [0.4.0], adds the previously missing [0.3.0], points [Unreleased] at v0.4.0...HEAD).