release: prepare v0.2.0

[eareimu]

Release prep

• Bumps the dhttp workspace packages to v0.2.0, including dhttp-identity, dhttp-home, dhttp-access, dhttp, and package metadata for @genmeta/dhttp / dhttpy.
• Keeps same-repository crates as workspace/path dependencies while converging cross-repo release dependencies to crates.io: dhttp-identity = "0.2.0", h3x = "0.4.0", and ddns = { package = "dyns", version = "0.4.0" }.
• Adds the DHTTP DNS plan/endpoint DNS construction line, endpoint DNS builder operations, listen-owned DNS publication behavior, and Endpoint::from_parts(...) for adapting existing H3 endpoints.
• Updates README dependency examples and package metadata for the v0.2.0 release line.

Release gates

• Release surfaces: crates.io packages dhttp-home, dhttp-access, and dhttp; npm package @genmeta/dhttp; PyPI package dhttpy.
• Already published in this wave: staged dhttp-identity 0.2.0, h3x 0.4.0, dyns 0.4.0, and dshell 0.4.0.
• Planned release tag: v0.2.0 after final PR CI and merge approval.
• Merge, tag, and publication remain blocked on full genmeta-test completion and explicit user approval.

Verification

Validated in a clean temporary tree without local .cargo patches:

• cargo metadata --format-version 1
• cargo fmt --all -- --check
• git diff --check -- . ':(exclude).cargo'
• TMPDIR=/tmp/dhttp-release-check.*/target/tmp cargo test --workspace --all-features --all-targets
• cargo clippy --all-targets --all-features -- -D warnings
• cargo publish --dry-run --locked -p dhttp-home -p dhttp-access -p dhttp