chore: release v0.1.28

[github-actions]

🤖 New release

• cryptify: 0.1.27 -> 0.1.28

Changelog

0.1.28 - 2026-06-04

Added

• (email) remove circle around signer-verified checkmark (#173)
• (email) replace unicode checkmark with inline PNG image (#172)
• (email) staging-only /staging/preview/ + shared render API (#171)
• (metrics) pre-seed known channels at zero on startup (#165)
• expose Prometheus /metrics endpoint for usage dashboards (#102)

Fixed

• (email) address postguard#197 deliverability + show disclosed signer name (#170)

Other

• bump pg-core 0.6.0 → 0.6.1 (#164)
• add semantic PR title check workflow (#162)

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This PR was generated with release-plz.

[dobby-coder]

Standard release-plz bump from 0.1.27 to 0.1.28. Diff is limited to version bumps in Cargo.toml/Cargo.lock and a changelog entry for the dependency lockfile update. Looks good.