Release Atelier-Kit v0.4.3

[gcomneno]

Summary

Prepare the v0.4.3 patch release for the scaffold safety fixes merged in #189 and #190.

Included fixes

• exclude generated Cargo/Tauri build artifacts from client scaffolds while preserving unrelated directories named target
• validate the Atelier-Kit source version before creating, replacing, or copying into a target
• preserve existing target contents when --force is used with an invalid source

Validation already completed

• npm test: 214 passed
• GitHub Actions CI passed for fix: exclude Cargo build artifacts from scaffolds #189 and fix: validate scaffold source before target mutation #190
• real writing-template scaffold: 3.3 MB
• desktop/src-tauri/target omitted
• desktop/src-tauri/Cargo.toml preserved
• git diff --check: passed

Scope

This release PR changes only CHANGELOG.md.