v0.2.0

• Add optional HTML email bodies while preserving a required plain-text fallback.
• Add optional file attachments restricted to configured allowed attachment roots.
• Add attachment count, per-file size, and total size limits through environment configuration.
• Keep one audited Gmail send path with no raw MIME, address, Cc, or Bcc input.
• Fix the recipient allowlist environment variable name to GMAIL_ALLOWED_RECIPIENTS.
• Add reusable GitHub workflows for CHANGELOG enforcement, version tags, and GitHub Releases.