feat(18-01): chi v5 dependency, go:embed static assets, HTML layout and overview templates

- Add chi v5.2.5 to go.mod
- Vendor htmx v2.0.4 minified JS in pkg/web/static/
- Create go:embed directives for static/ and templates/
- Create layout.html with nav bar and Tailwind CDN
- Create overview.html with stat cards and findings table

pkg/web/embed.go

@@ -0,0 +1,14 @@
+package web
+
+import "embed"
+
+// staticFiles holds the vendored static assets (htmx.min.js, style.css, etc.)
+// embedded at compile time.
+//
+//go:embed static/*
+var staticFiles embed.FS
+
+// templateFiles holds HTML templates embedded at compile time.
+//
+//go:embed templates/*
+var templateFiles embed.FS