Prepare dhttp v0.4.0 release

[eareimu]

Summary

• Prepare the dhttp workspace release at v0.4.0.
• Publish dhttp-access as 0.3.0 so access-control ORM APIs use the same dhttp-home 0.3.0 type line as the facade.
• Keep npm/PyPI package metadata aligned with the workspace version.

Release surfaces

• crates.io: dhttp 0.4.0, dhttp-access 0.3.0; already-published unchanged crate versions should be skipped by the workflow.
• npm: @genmeta/dhttp 0.4.0.
• PyPI: dhttpy 0.4.0.

Verification

• cargo +nightly fmt -- --check
• cargo +stable semver-checks --manifest-path access/Cargo.toml --baseline-version 0.2.0 --all-features
• cargo +stable semver-checks --manifest-path dhttp/Cargo.toml --baseline-version 0.3.0 --all-features
• cargo +nightly clippy --all-targets --all-features -- -D warnings
• cargo +nightly test --workspace --all-targets --all-features