chore: prepare gateway v0.7.0 release

[eareimu]

Summary

• Prepare the gateway/pishoo release as v0.7.0 based on cargo-semver-checks results.
• Align release manifests with dhttp 0.4.0.
• Harden release packaging CI for workspace-member metadata resolution and RPM base-image pulls.
• Update the changelog component summary.

Release surfaces

• Product packages: DEB, RPM, and Homebrew through the S3/R2 release workflow.

Version plan

• gateway 0.7.0
• pishoo 0.7.0
• pishoo-common 0.5.1-1

Local verification

• cargo +stable semver-checks --manifest-path gateway/Cargo.toml --baseline-rev v0.6.0 --all-features
• cargo +stable semver-checks --manifest-path pishoo/Cargo.toml --baseline-rev v0.6.0 --all-features
• cargo +nightly fmt -- --check
• cargo +nightly clippy --all-targets --all-features -- -D warnings
• cargo +nightly test --all-targets --all-features
• cargo +nightly test -p xtask
• cargo +nightly clippy -p xtask --all-targets -- -D warnings