ModelCraft foundation: workspace, quality gates, FE model, command engine, geometry boundary

A pure-Rust CAE modeling workspace following the SolidCraft conventions:
- modelcraft-model: nodes and elements by label with hostile-input validation
- modelcraft-geometry: SolidCraft's kernel (pinned git dependency) behind our own API;
  tessellation into a face-tagged boundary surface for volume meshing
- modelcraft-engine: CommandSpec registry, Session::execute with rollback and panic guard,
  scripts and a journal
- modelcraft-cli: list commands, run scripts
- xtask: layers (only geometry may use solidcraft-*), assets, licences, tests, wasm, ci
- AGENTS.md, architecture, ADR 0001 (libraries and licences), roadmap, CI

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

SECURITY.md

@@ -0,0 +1,11 @@
+# Security policy
+
+ModelCraft is young; only `main` and the latest release get fixes.
+
+Please **don't open a public issue** for a security problem. Report it privately through the
+repository's [Security tab](https://github.com/jyviko/modelcraft/security/advisories/new) with
+what you found, how to reproduce it (a model, deck or script), the version and platform, and the
+impact you expect.
+
+Reports are especially useful for opening untrusted models, decks or scripts (crashes, runaway
+memory or CPU, path tricks) and for the control channel once it exists.