v0.4.2

Patch release. Headline: the container build is restored — ghcr.io/glentner/xdu:latest
republishes from this version with all four binaries, including xdu-rm.

Fixes

• Restore container build with explicit C++ toolchain (#13) — the slim builder ships no
  tool literally named c++, so the bundled-DuckDB compile aborted; the builder now installs
  g++ with the requirement stated at the install, and both build jobs have timeout headroom.
• Make xdu-rm --limit selection deterministic (ORDER BY on every limited deletion).
• Statically link the Parquet reader; rm_tests drives the built binary (no more stale-binary
  green suite, no DuckDB extension autoinstall on air-gapped nodes).
• Make the man-page literal gate assert content, not layout (whitespace-normalized matching;
  duplicated literals asserted by count).

Refactor

• Harden and optimize the index-build crawl (#9).
• Remove cruft.sh example script.

Docs

• Repurpose ROADMAP.md into a forward-looking feature roadmap.
• Record the CI-red root cause and the stale-binary test defect.
• Add a Prose and comments directive with commit widths.

Harness

• Adopt spec-driven software factory; commit-msg hook reflows bodies to 80 columns.
• Review-gate hardening (human sign-off, build-state cleanliness, CI-rollup gating, and more —
  see the [harness] commits since v0.4.1).