pipeline v4.2.0

First minor release of the v4 line.

Changed (BREAKING):
- Removed legacy templates: rust-cli@v2.x, agent-shape@v2.x,
  latex-paper@v1.0.0. Consumers must migrate to v4 meta-components
  (tool-rust / lib-rust / latex-template) before referencing
  components from this release.

Added:
- hygiene gate's disable_default_forbidden bool input. When true,
  skips DEFAULT_FORBIDDEN regex list. For repos whose primary
  artifacts legitimately match a default pattern (e.g.
  sysml-bench-results ships *.log benchmark artifacts).

Fixed:
- latex-template screenshot-pdfs uses basename so it resolves PDF
  paths consistently with where build-pdfs moves them in v4.1.7+.
  Was looking at latex/example-academic.pdf; real file is at
  example-academic.pdf in project root.

Lockstep version bump v4.1.10 -> v4.2.0.