chore: prepare gmutils v0.6.1 release

[eareimu]

Summary

• Align gmutils release manifests with dhttp 0.4.0 and dhttp-access 0.3.0.
• Re-select published crate versions from cargo-semver-checks results.
• Update the v0.6.1 changelog component summary.
• Keep the welcome onboarding group gate compatible with Apple targets.

Release surfaces

• crates.io: gmutils workspace crates except xtask, with already-published versions skipped by the workflow.
• Product packages: DEB, RPM, Scoop, and Homebrew through the S3/R2 release workflow.

Version plan

• genmeta 0.6.1 (binary-only; cargo-semver-checks not applicable)
• genmeta-curl 0.6.0
• genmeta-ssh 0.6.1
• genmeta-access 0.3.0
• genmeta-identity 0.3.0
• genmeta-proxy 0.3.0
• genmeta-discover 0.3.1
• genmeta-doctor 0.3.1
• genmeta-nat 0.4.0
• genmeta-nslookup 0.4.0

Local verification

• cargo +stable semver-checks ... for each publishable library crate with the selected version plan
• cargo +nightly fmt -- --check
• cargo +nightly clippy --all-targets --all-features -- -D warnings
• cargo +nightly test --all-targets --all-features
• cargo +nightly check -p genmeta-identity --all-features
• cargo +nightly clippy -p genmeta-identity --all-targets --all-features -- -D warnings
• cargo +nightly test -p genmeta-identity --all-features

[eareimu]

Superseded by #8 for the v0.7.0 release branch.