Add quality-matrix implementation to pdftract-ci with msrv-check step
using rust:1.78-slim to detect usage of newer Rust features.
Changes:
- .ci/argo-workflows/pdftract-ci.yaml: Implement quality-matrix DAG with
msrv-check, clippy-fmt, and cargo-audit templates
- CHANGELOG.md: New file documenting MSRV bump policy (MINOR version
event, warning period, update checklist)
The MSRV gate prevents silent drift that would break downstream consumers
on older toolchains. Any Rust 1.79+ feature (e.g., let-else, core::error::Error)
will fail the msrv-check step, triggering a policy review.
See notes/pdftract-2w02.md for acceptance criteria verification.
Co-Authored-By: Claude Code <noreply@anthropic.com>
