Seed repository: rev-8.0.0 reference, frozen oracle, toolchain, test harness

Reference implementation of the strap-beam generators at revision 8.0.0, kept
so the acceptance oracle can be regenerated. Not a live target; the running
application has no OpenSCAD dependency.

The oracle holds 123 frozen cases, 113 accepted and 10 rejected, produced by
OpenSCAD 2021.01 with BOSL2 at 92d697c2. The ten rejections are part of the
contract: a port that accepts them is wrong.

tests/test_oracle.py specifies the port API and was written before the port,
so the interface follows from what must be verified rather than what is
convenient to implement. Proven by adversarial stub: a build() that rejects
everything passes all 10 rejection tests and fails all 226 acceptance tests.

.gitignore

@@ -0,0 +1,30 @@
+# Virtual environment — a legitimate artifact inside install_dir, never tracked.
+venv/
+.venv/
+
+# Python
+__pycache__/
+*.py[cod]
+*.egg-info/
+.pytest_cache/
+.coverage
+htmlcov/
+
+# Instance configuration — never committed. See docs/ENVIRONMENT.md section 13.
+deploy/site.env
+
+# Generated output
+/out/
+*.stl
+*.step
+
+# Shell history from interactive sessions
+.lesshst
+
+# Service user's HOME is install_dir, so caches land here
+.cache/
+.local/
+
+# Service user HOME is install_dir, so SSH keys land here
+.ssh/
+.gitconfig