New

• dmarc: bind DMARC reports to customer accounts for multi-tenant filtering #43
• worker: receive and display DMARC aggregate reports
• dashboard: DKIM-sign system emails for improved deliverability
• tests: add E2E tests for system email delivery
• dashboard: deliver system emails via direct MX resolution
• docker: unify Dockerfiles with cargo-chef, sccache and registry cache

Fixed

• dashboard: use correct DKIM selector "euromail" for system emails
• api: log version on startup for deployment verification
• dashboard: apply rustfmt to system_email module
• docker: bump Rust base image to 1.88-bookworm
• docker: pin Rust base image to 1.85-bookworm for reproducible builds
• deploy: update image tag to v1.12.1 for Flux deployment
• ci: add workflow_dispatch trigger to Release workflow
• docker: add OCI source label to link GHCR packages to repository