Release 0.4.0

[AnlangA]

Summary

• Bump bbcom version metadata to 0.4.0 across package.json, Tauri config, Cargo.toml, and Cargo.lock.
• Move current changelog entries under the 0.4.0 release heading dated 2026-06-17.
• Keep the v0.4.0 tag pointing at the release commit so the tag-triggered release workflow can build artifacts.

Validation

• pnpm run build
• cargo test --manifest-path src-tauri/Cargo.toml