build: add test report generator (task 0003)

Add scripts/test-report.ts (bun run test:report): it runs the full suite
with JUnit + lcov output, then renders a gitignored reports/test-report.md
— a summary, a describe-grouped inventory (pass/todo/fail), and a
coverage table. The report is written even when tests fail and the script
exits with the test run's own status, so CI can gate on it later. Adds
fast-xml-parser (dev) for robust JUnit parsing; lcov is parsed by hand.

package.json

@@ -9,6 +9,7 @@
   "scripts": {
     "test": "bun test",
     "test:coverage": "bun test --coverage",
+    "test:report": "bun run scripts/test-report.ts",
     "lint": "biome check .",
     "format": "biome check --write .",
     "postinstall": "bun2nix -o bun.nix"
@@ -16,6 +17,7 @@
   "devDependencies": {
     "@biomejs/biome": "^2.5.3",
     "bun-types": "latest",
-    "bun2nix": "^2.1.2"
+    "bun2nix": "^2.1.2",
+    "fast-xml-parser": "^5.10.1"
   }
 }