Add CLAUDE.md and the test harness

CLAUDE.md records the Nova constraints this extension is built around —
established by reading Nova 14.1's bundle and probing its preview server,
and expensive to re-derive: no previewer extension point, generated pages
must live under the preview root, dot-directories are served, and no API
reaches into a preview WebView. It also flags the one unverified
assumption, that a tab showing Preview still appears in
nova.workspace.textEditors, with its symptom and fix.

Tests/ is the harness that built the extension, kept rather than left in a
scratchpad: a stubbed Nova runtime backed by the real filesystem, node
suites for generation and the four close paths, and a headless-browser
render test that skips itself without a browser. It caught the ./ doubling
in rebased links and checkbox state not surviving serialization.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TueXpMi7eAtgWPuMr4ii52

Tests/run.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+# Runs every test. No dependencies beyond node; render.test.js additionally
+# wants a headless browser and skips itself without one.
+set -eu
+cd "$(dirname "$0")"
+
+echo "— syntax —"
+for f in ../Scripts/*.js ../Assets/preview.js ./*.js; do node --check "$f"; done
+python3 -c "import json; json.load(open('../extension.json'))"
+echo "ok"
+
+for test in generate close render; do
+    echo "— $test —"
+    node "$test.test.js"
+done