feat(okf): add minimal okf_viz Cytoscape generator with tests

Full suite green (20 tests). Smoke-tested on Google crypto_bitcoin bundle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

custom-skills/97-ourdigital-okf/code/scripts/tests/test_okf_viz.py

@@ -0,0 +1,36 @@
+import sys, tempfile, unittest
+from pathlib import Path
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+from okf_viz import build_graph, render_html, main
+
+FIX = Path(__file__).resolve().parent / "fixtures" / "mini_bundle"
+
+
+class TestViz(unittest.TestCase):
+    def test_build_graph_nodes_and_edges(self):
+        g = build_graph(FIX)
+        ids = {n["id"] for n in g["nodes"]}
+        self.assertIn("tables/orders", ids)
+        self.assertTrue(any(e["source"] == "tables/orders" and e["target"] == "tables/customers"
+                            for e in g["edges"]))
+
+    def test_render_html_embeds_data_and_cdn(self):
+        html = render_html(build_graph(FIX), "Mini")
+        self.assertIn("cytoscape", html)
+        self.assertIn('"nodes"', html)
+
+    def test_render_html_escapes_script_close(self):
+        g = {"nodes": [{"id": "x", "type": "T", "title": "x",
+                        "description": "", "body": "</script><b>hi</b>"}], "edges": []}
+        html = render_html(g, "X")
+        self.assertNotIn("</script><b>hi", html)
+
+    def test_main_writes_file(self):
+        with tempfile.TemporaryDirectory() as d:
+            out = Path(d) / "v.html"
+            self.assertEqual(main(["--bundle", str(FIX), "--out", str(out)]), 0)
+            self.assertTrue(out.exists() and out.stat().st_size > 500)
+
+
+if __name__ == "__main__":
+    unittest.main()